In the documentary, the two Edies seem resigned to their reduced circumstances, all things considered.
The 'clean-up' of the mansion (supposedly taking place at time of filming) is not much in evidence, apart from a lunkish and slightly stunned-looking young carpenter/houseboy whom Little Edie (sashaying about in her 'costumes' and trademark headwrap) calls, incongruously, the 'marble faun'.
Mother and daughter are happy enough to share their home with 'a few too many cats' (neither spayed nor housebroken) and with the wild racoons that have eaten the shingles off the roof and invaded the attic.
Time, in the film, is marked by the ever-growing holes in the walls. But - untroubled by the damage - Little Edie totters up the dark stairs in her high heels with big sacks of Wonder Bread and Cat Chow for the raccoons, which she dumps out on the attic floor. ('Of course, I'm mad about animals, but raccoons and cats can become a little bit boring. I mean… after a time.')
As her imperious mother shouts orders from her bed, and scolds her daughter for failing to marry a Getty when she had the chance, Little Edie (52, at time of filming) gets herself up in various eye-popping ensembles from the ragbag, stands atop the scales peering woefully down at her weight with opera glasses ('Isn't it awful when a dancer gets fat?') and cheerfully performs her famous Virginia Military Institute dance (complete with American flag) for the camera.
(The Virginia Military Institute dance is particularly beloved by fans of the film; readers with high-speed computer access may go to YouTube and find various versions of it online.)
Amid the daily routine at Grey Gardens - which is at once macabre and charming, in the manner of Edward Gorey - a great, unspoken question throws its shadow over the film.
How did this patrician mother-and-daughter pair with their tony accents and their Kennedy connections slide down so hard and fast from the heights of the Social Register (its broad As still clearly audible in their voices) into such flagrant ruin?
The short answer is that the elder of the two Edies - blowsy, bedridden chanteuse in smudgy harlequin glasses and a floppy hat, who famously entertains guests in one sequence by boiling up ears of corn on a bedside hot plate - was a bohemian socialite who, in the 1930s, alienated her husband and father by hiring an accompanist and entering into a career as a nightclub entertainer: something not done by women in her set.
Her husband was glad to seize upon an excuse to leave her; her father disinherited her. On the litter-strewn floor by Big Edie's bed (which she seldom leaves) is propped a grand portrait in the style of Sargent, from back when she was still Edith Bouvier.
No matter how many times you have seen the film, the image shocks, for it does not seem possible that this cool, gowned society beauty with pearls, straight from The Philadelphia Story, could have wound up as the dotty old wreck surrounded by trash and singing in bed.
But before the shock of the transformation can register, one of the Beales' many cats slinks behind the portrait to urinate. 'Oh, look,' says Big Edie, 'the cat's going to the bathroom on my portrait,' and then adds tartly: 'I'm glad somebody's doing what he wants to do.'
It is even more difficult to understand exactly how Little Edie, who once had a promising career as a model, slipped into poverty and madness alongside her mother.
In photographs and old news clippings, we see her as a long-legged and gorgeous young débutante, much more striking than her cousins Jacqueline and Lee Radziwill.
('See how beautiful Edie was when she was young?' her mother comments. 'It's perfectly foolish of her not to look that way now.')
Little Edie's story - repeated passionately again and again - is that she had to leave New York to come home and look after her mother, and that she never married because sharp-tongued Mrs Beale managed to run off all the suitors who came along.
It's a perfectly probable scenario - and yet it does not fully explain why mother and daughter have retreated into quite such a squalid and isolated life, having hardly left the house in 20 years - 'kind of locked up', as Albert Maysles has said, 'but by their own choice'.
If all this sounds unlikely material for a Broadway musical or a Hollywood film (one is in the works, starring Jessica Lange and Drew Barrymore), it is.
Grey Gardens is such an unsettling portrait of folie à deux that most people are puzzled and disturbed the first time they see it. Its charms tend to emerge after a second viewing, and people who love it tend to have watched it so many times they know it practically by heart.
In America it has a devoted cult audience, particularly in the fashion world. An incidental delight of the film is Little Edie's utterly singular mode of dress, which inspired a famous Steven Meisel photo-shoot for Italian Vogue in 1999 and, more recently, a 2002 feature in American Vogue with the model Karen Elson.
The designer John Bartlett, who is interviewed along with Todd Oldham on the Criterion DVD, based his autumn 2000 collection on what Little Edie blithely calls her 'revolutionary costume': tights over shorts; bath towels as headscarves and skirts worn upside-down or as capes; long-sleeved woollen sweaters wrapped turban-style around the head and fastened with giant rhinestone brooches.
It all looks as batty as it sounds - yet there's an uncanny rightness about it, too, a sureness of proportion, as if Miuccia Prada or Marc Jacobs had dressed her out of bins.
But it is Big Edie and Little Edie themselves, and the messy, many-layered intricacies of their relationship, that make this a film to return to.
On every viewing, there is something new to notice, an almost literary richness which suggests not only Miss Havisham but other, gentler Dickensian eccentrics fallen on hard times, such as ruined Miss Flite with her 'reticule' and her garret full of birdcages. (With their theatrical pasts, and their readiness to sing and dance at the drop of a hat, the Beales could also have been employed brilliantly on the stage by Mr Crummles in Nicholas Nickleby).
But mother and daughter are perhaps most Dickensian in their speech, which is incredibly comical and stylised, surreal at times, full of hyperbole and distinctive tics.
Big Edie, with her haughty, piercing voice, is a matriarch out of a screwball 1930s comedy gone terribly wrong; Little Edie (who often calls her mother Mrs Beale) speaks in a daffy, antiquated schoolgirl slang straight out of Miss Porter's.
They are constantly berating and correcting each other, talking at the same time, murmuring behind each other's backs, and - in asides to the camera - appealing to the Maysles brothers, whom they both plainly adore.
'The people don't speak,' Little Edie whispers fretfully to the Maysles, drawing them aside, in the midst of her mother's monologue about how 'terribly happy' her failed marriage was. 'But they don't get divorced.'
Big Edie overhears this: 'I had a terribly successful marriage!'
'There was a fake Mexican divorce,' Little Edie murmurs. 'He did have another wife that we didn't recognise... it wasn't recognised by the Catholic church...'
'I never had a fight in my life!' her mother shrills. 'I never threw anything at Mr Beale!' Back and forth it goes, as fast and funny at times as a vaudeville routine.
Yet their fixation on the past is also rank with a repellent, nightmarish quality. The house itself - falling to pieces, packed with mildewed and crumbling 'mementos' - is a visible manifestation of their shared compulsion to clutch too tightly, to hang on, to endlessly repeat old grievances and complaints, so that even in its campier and more charming moments, their banter is alight with a fierce glint of insanity.
Edith Sitwell attributes the English predisposition to eccentricity to the 'peculiar and satisfactory knowledge of infallibility that is the hallmark and birthright of the English nation'.
And part of the reason Grey Gardens is such a disturbing film is the utter self-assurance of the Beales.
Their sense of themselves - and of each other - is unshakeable; like ageing drag queens in a Diane Arbus photograph, they seem to have no conception how grotesque they appear to the viewer.
Yet - and this is what Dickens would have loved most about the Beales - there is a deep, endearing humanity in how stubbornly they cling to their romantic vision of themselves.
'You don't see me as I see myself,' confides Little Edie to the Maysles at one point, 'but you're very good at what you do see me as.'
In this unflinching but affectionate documentary we see mother and daughter not only as they are, but as they would like to be - and as the unlikely fashion icons and inspirations for stage and screen they have become 30 years later.