I think that's it if you distill it down to its most basic. I suppose its pretty hard to pin down what makes something collectable but I do agree with what you said about geometry vs. construction materials....and bikes that ride well aren't necessarily collectable...or not collectable...In some cases bikes are more sought after because of who made 'em....other cases who rode 'em...other cases just because of their place in time and history.

I think my Team Miyata is my favorite (in terms of ride quality) of all my bikes. The components are a hodgepodge of middle of the road stuff but IMHO the frame is what really makes that bike great. I'm not sure if its the Splined and butted Cr-Mo tubing (although that certainly helps bring the weight down) or the Geometry or what but if you could copy that bike's ride and feel and make me a version that took wide tires and fenders I'd have my dream machine.