It's a tough question that deserves thought. What one can do (or not) isn't the same as what one should do (or not).

I'd love to own an early '70's PX10, for example. But as configured from the factory it wouldn't be a good bike for me. I'd want to lower the gearing and swap out the Simple derailleurs, the tubular tires, maybe the saddle too. I could keep the parts, but if I never intended to sell the bike they'd just be collecting dust in a box. Now, if someone else had already done that then I'd consider owning. Otherwise I'll let a collector buy it. I don't want to do those things, especially if someone else went through all the trouble to restore it.