I'm generally with Cram. I wear clothes if I like the way they look and I connect with them on some level. If a shirt is for a specific concert I wasn't at, I probably wouldn't buy it because I wouldn't "connect" with it. But there are exceptions. Like with the Boston Maiden shirt posted in the Maiden thread, for example, despite being in California and being nowhere near that show at the time it happened, it's a really cool shirt, and it appeals not only to the Maiden fan in me, but also the American history buff in me that is very much into revolutionary war history. So I'd buy that shirt in a heartbeat.
With a vintage shirt, it's kinda the same thing. If it is a shirt that celebrates a landmark time in a band's history, and I connect with celebrating that history, I think it's cool to wear the shirt whether I was there or not. I'm not trying to represent as "Look at how cool I am! I was THERE!" I'm just memorializing something that I think is cool, that's all. Not really sure why that is a problem for some.