Historically (before the romantic period) artists/writers/thinkers/etc. have been obsessed with the idea of perfection just as they have been obsessed with the idea fo attaining holiness, proof of God on earth. A quote from Kant:
"The judgment of taste is entirely independent of the concept of perfection."
There are undoubtedly cultures that have existed or do exist that may find the David in poor taste, or lacking. Picasso for example found beauty in what was ugly, deformed. Impressionist painters went out of their way to depict a surreal state of life (as do Korie and Frankel and Wright).
Arguably (as many early thinkers thought) perfection is not desirable because it means the end. Once you have created the perfect piece of art, what need is there to continue? The perfect book? The perfect life? Many, myself included, feel that there is much beauty in imperfection, because everything is in some way imperfect.
Perfection is a philosophical concept and no person holds the same standards for it. Therefore, no art is perfect.
If perfection is a mathematical concept or the perfect achievement of a set of rules (say, dramatic aristotelian rules), then Grey Gardens is an incredibly imperfect musical because it completely subverts the tradition even as it upholds it. I would say that the things that make Grey Gardens imperfect are some of what you love about it. Personally, I think it's really childish to even use the word perfection. What the heck is it even supposed to MEAN, besides in the most general, buzzwordish sense?
yr ronin,
joey