I think the biggest bottom line here, is that nothing turns into an antique overnight...I think c4's and 5's both will see a long period of time as an affordable used car, I think with both you'll have some of the "get what you pay for" where you'll be able to find cars that are cherry if you want to pay for it, selling one of such cars will be possible, but take patience and time to find the buyer who understands and appreciates a car in such condition....and is willing to pay for it. I also believe that whether driven, or garage queens, ones kept up will some day pay off for those who hang onto them, and those who don't will often fall into the "I wish I used to have a...xxxxx...wish I hadn't sold that car...".
The pricelessness to me isn't what the blue book or monetary value is, it's the joy in driving it and the friendships that come into place because of it. Drive on!