3 mods come to mind.
1. On the older small flippers, I put a 1 inch rubber in the groove, and 1.25 inch rubber just below that.
2. Gottlieb tilt bobs are cut off abruptly at the top so I put a small fishing sinker above that for more tilt adjustability
3. On an old Jack in the Box (http://ipdb.org/search.pl?any=jack+in+the+box&sortby=name&search=Search+Database&searchtype=quick#1329) I rewired it so that after knocking down all the drop targets, the top flippers were reversed so the top left flipped with the bottom right. After knocking down a second time, the top left and bottom right were actuated by the left flipper button.