While I'm not sure that the two point of your question are related, I will take a stab at the first.

I think modern classics are the bikes that, for some reason or other, staying power. Sure, some new bikes are going to get thrown away, but others will probably continue to be sought after. They will get dug up over and over again. People will likely post threads like, "Can anybody tell me about this BMC?" or "Cervelo at a garage sale, any good?". The thread will have people post things like:

First poster:

"Nice bike! I have two Giant TCR SLs, both with older Dura Ace (7900), and I gotta say they get the job done. Their not as good as X, but can hold their own in a race and make great commuter. The best part is, that these frames were made with 130mm rear spacing so you can upgrade to a modern 1x20 internal gear hub and save some weight. "

Second poster:

"Yeah, $50 ain't bad. It looks like that drive side belt stay is cracked. You'll want to go to the LBS and get that rebonded before you ride it much. Shouldn't cost about $90 to have it done, but it will be worth it, since you should probably be able to get around $250-$300 for it depending on location."

Third poster:

"Don't listen to him! Your frame is damaged beyond repair! Only CDC (Center for Damage Control) certified persons can handle that frame. Never fear, I am certified and will dispose of it properly, at no cost to you. "