And don't forget lots of well fleshed out, non powered (or lower powered) npcs (e.g. the mayor, the police chief, some beat cops, EMTs, the barrista at the local Starbolt's coffee shop). People the pcs are likely to encounter other than just other npc superheroes.
One other thought, if a gadget and/or vehicle book isn't needed....I would settle for just having it be a section in a book. And please don't forget the mecha. Gotta have mecha!