If you're still wondering about Robotron, etc., yes you can use the first and second player sticks to control it. Just a matter of where they're placed, and if it's comfortable to use them both at the same time. (i.e., might be tricky if the steering wheel is in between them)
I think it's worth having 6 buttons on each joystick to play mortal kombat and street fighter variants. If you don't want those, you can hold off fine with 4 and save a few inches of panel. You might consider getting joysticks with a top fire button, for games where you need combos like spinner+joystick+button, or 2-joysticks+buttons. (Tron, Battle Zone...) I like the Happ top fire button joysticks a lot. They're constructed just like the Supers, but with an extra button mechanism, and you can use ctrlr files to have Mame ignore the top button unless the game needs it.