Yeah I wouldn't ever make changes that couldn't be reversed but in most cases I find I'm replacing a worn out or damaged part so there is nothing really to save. If a future owner wanted to return it to absolute original condition he'd have to buy the new NOS stuff anyway.

...unless you're of the persuasion where you belive you need to have the original part even if it's worn out or damaged but I see no reason to keep a worn out chain or a pitted spindle unless I'm working on Fausto's or Eddie's bike and in that case I wouldn't be doing any restification anyway.