I can understand for genuinely rare parts, for me those would be Sugino 400 cranks, Harry Leary Turbo bits or chrome 7x rims for instance, but parts that were fitted far more widely and more commonly? If my financial situation was a better I would be chasing 400 cranks for my Laserlite, so I would be adding to the price inflation of those I guess but the more common parts, I won't pay those prices!
I have 4 completes in my living room and I guess it will never be 5, at least in the current, and prolonged climate. I do have a frame in the spare room but no parts to build it up. Anyway, I still enjoy visiting here everyday.