Yeh. I'd probably still be resetting for shiny Dratini if I could've only bought two per sit. The only ones that make any real difference are Dratini, Porygon, and (arugably) the bugs.
I have fire red and am still trying to get porygon. It aint easy i tell ya, but its probably worth it. Personnaly i prefer catching Dratini in the safari zone. But that's me.