Like Karin, I've bought things that looked vintage in cut/style, just because I liked them. They weren't specifically "repro" or even vintage-inspired (a la the current Mad Men line at Banana Republic). An example is an Isaac Mizrahi for Target dress I bought for about $35 several years ago. Decidedly vintage silhouette (nipped waist, wide neckline with short sleeves, full skirt). It is incredibly well made, regardless of the price, which is likely a fluke, given that most Target stuff disintegrates in a matter of weeks, of course. It was certainly the bargain of the century. Can't find a photo of it.
As for reproductions, well, if you were (or hired) a good seamstress/tailor, that person could reproduce any vintage design you wanted just as well and easily as they could any modern design (either by copying an existing dress or working from a vintage pattern). The quality would depend entirely on the fabrics you chose and the skill of the tailor. The bonus would be that you could, as noted above, make the garment comfy (1% lycra makes all the difference, doesn't it?), washable, etc., without sacrificing excellent construction.
So now I think I've talked myself into having someone make me a dress from a vintage pattern. LOL. But somehow, it just wouldn't be the same. No, I don't think I'd buy "repro" INSTEAD of real vintage, because it doesn't have the history. There's no story (known or unknown) behind a new dress. I'm sentimental about that aspect of vintage. I also wouldn't have something reproduced to prevent a vintage dress from being "used up." Can't take it with you, after all. And unless it belongs in a museum, or you are saving it specifically to pass down through your family or similar, it belongs on a body (IMHO).