I am going a bit broader and just lumping the original run and the reprints together as the run I'm going after now. I know I'll eventually want both and that 1/2 the time the books I pick up are due to what I feel is a favorable price presenting itself to me. The rest of the time are those books that I actively seek out.
My eyes are constantly wandering, though, and I'm pretty bad at picking books up that are outside of 1-93, whether it be upgrades to later runs, pretty slabs, or whathaveyou. The one thing I am squarely focused on is the grade I'd like to stay within for each era, and I am aiming to pick up 1-3 SA books a month depending on what's going on in life. Definitely not in a rush - wouldn't be able to be in one even if I wanted. If you miss out on a book, there will most likely be another book out there that interest you, which is great. Or maddening.
I can give myself temporary boundaries to play within, but in reality there is no stopping point.
Donald