Oh man, Miller's DD has been going DOWN. Even the biggest key:
It's not like all collectors have infinite amount of money. If something else is hot, they will just gravitate towards something else, selling off what is not hot and so some books will go down while others go up. I would be very curious to see how well Ultimate Fallout 4 does in 20 years from now.
When it comes to first appearances, you still have to rely on scarcity and demand. Because saying a blanket statement that you can't go wrong with first appearance will leave you like this.
Sold May 2016:
Sold July 2020:
And I wont leave the OP hanging, if you want to get a headache, check the fluctuating prices on the 3 books battling to be the main book to own for Kamala Khan.