The vast majority of bikes from 30 years ago were also crap. Most of them are long gone. The decent ones are still getting ridden. I got 3 decent frames from the 70s last summer for free. One of them is a Raleigh witth Reynolds 531 main triangle. Adjusting for inflation, I bet that bike cost around $1000 of today's dollars brand new. In other words high quality, but not exotic. It's only the exotics from the 1970s that demand high prices,a nd it's only the exotics from today that will demand high prices in 30 years when the vast majority of today's mass produced bikes will be scrap.
As far as Carbon goes, I doubt if many well-ridden carbon frame swill last 30 years. It only takes one good nick to wreck a carbon frame. the vintage ones that survive in tact will most likely be worth quite a lot due to their rarity.