I agree 100% with the flood of books that noone wants. This is why I just toss most low grade SA books (or mid grade Dell/Gold Key or others) in my $1 boxes. The funny thing is, a lot of them still sit for ages as run collectors have been a dying breed since the early to mid 00s.
Just like other collectibles, the A tier keys will across all age groups will hold their value longer term as they are more widely accepted as investment collectibles, not just collectible comic books. For the past decade I have seen the evolution of teenagers that buy moderns, then Copper Keys (e.g. 1st Harley, Venom or Deadpool) and then move back to BA, SA, and even GA keys when they start earning decent wages. It is fun to see these new collectors "grow up" over the years.