IMHO, like so many other rings in life, it's a choice that can be based both on logic as well as common sense. If the frame suits you, if it has the braze-ons you want, if it is exactly your size — you in the zone. Now the clincher: there should be no surprises. No rust inside the tubing. The steering tube is not partly stripped. No one has mandrelled the hell out of the seat tube to get a post to fit. You don't need a frame-maker to check or realign it. The BB and head tube do not need to be refaced. It's never been crashed. New paint. The decals are all there. If all that turns you on, it looks like a good thing. Sure you pay out some dosh, but you get something new.