Wu-tangled's threads are very thought-provoking. I think in a way he touches a nerve, like perhaps a few here were didn't have money to collect the stuff they loved in their youth. Probably a few of them went through a time in their late 20s when they came into some money, but an overwhelming sense of responsibility prevented them from spending it on what they really wanted; rather it went to things like car payments, mortgages, etc. But maybe now that people later on in life have found some sort of comfortably equilibrium with their finances, there's some room for retro bikes and bike parts.
Personally, for me, they way I justify it to whoever, myself, my girlfriend, my co-workers (when things like $300 ten year old Ringle wheelsets arrive at the office) is that if it wasn't bikes, it'd be something else.
Everyone has to have some sort of hobby.
It does get tough, especially for, since my license still says pro mtb'er, to justify working on old bikes when I should be out training. But I think I've found my equilibrium.