My three daughters are into collecting vinyl, ages 15-20.
From my limited experience looking for records to flesh out their collections, they (and their friends) value classic artists like Hendrix, Doors, Beatles, Pink Floyd, Bowie, Kinks.
With respect to the Kinks as an example, you can get as many Sleepwalker copies as you could possibly want but just try to find Arthur or Something Else or Village Green. With Bowie, you can get Let's Dance but will have more trouble finding Ziggy Stardust and even more trouble finding Hunky Dory.
I guess the 70's and late 60's titles are harder to find. When I ask vendors about where these disks are, I've been told they were widely available, say, 5 yrs ago, but now fly out the door with the resurgence in vinyl. My 15 year old saved up and paid 50 bucks for sealed versions of Bowie's Hunky Dory and Space Oddity. Could this depraved music hobby possibly be genetically transmitted???