I almost bought the AC/DC topper, but then it would be the only pin I own with a topper (my GnR doesn't have one). I decided I would rather use that money for a shaker. I was getting kinda caught up with the mod planning for a while, but then I played some machines on route and realized I had just as much fun playing the unmodded ones. I finally figured out my priority for mods:

Must have: LEDs, LED OCD (and GI OCD when released), shaker, pingulp
NIce: under cab lighting tied to flashers (adds a lot to the game when playing in a dark room)

That is pretty much it for me. LIghts, shaking, and beer holder.