I've been on both sides of this.

For the most part- if you've got something rare and something durable (likely to outlast you)- you do have sort of a responsibility to take care and preserve it. There's that episode here with the dude who scored a 59 Paramount for $200. He sees a $200 bike to permanently customize, not an exceptionally really rare bike that people would go to great lengths to own.

But there are some that just turn out so unbelievably cool. I love old touring bikes- I like to leave them very stock- I haven't even changed my bikes over to 700C yet. Yesterday, I saw a web page of a Specialized Expedition. The guy stripped the paint, moved the brake braze ons, added braze ons, nickel plated it- it was AWE INSPIRING.

However, there are some that it's just "it's time."