I do a big shop twice a year (spring and fall) which includes some designer items--shoes, clothes, or both. (I do a baby shop in the summer/winter which typically does not.) If I can find what I want in a diffusion line, I'm all over it. Buying "real" designer clothes really burns through your budget quickly and, obviously, automatically cuts back on the number of pieces you can buy. IMO, designer is worth it because of the statement, which you just don't get from mainstream department store brands (which I think are fine for filler pieces or basics). I agree with everyone who's said designer shoes are probably the best designer buy. If you coordinate your wardrobe well, you can wear the same statement shoes in very different ways multiples times a week. I would say the style differential is quite a bit more noticeable than the quality differential.
I liked that Valentino dedicated a recent collection to Everywoman (actually I think he said "the woman of the streets" which can mean something a bit different over here
) ... he said that this woman can only afford one Valentino, but she can wear it with a thousand other things.
Well, one of my designer buys for spring was a pair of Valentino shoes--I think the most I've ever spent on shoes. I haven't been tremendously pleased by how they've worn, and would love to chat with Valentino for a moment about the fact that Everywoman actually walks around and isn't carried in a litter
As far as sales, I don't have the patience for it. I have to channel all my patience into finding the right item, and once I've done that, I don't want to roll the dice that it will still be available at sale time. After all, it's not a secret to anyone else what's the best stuff, and I wear common sizes