The way I look at it is that yes, the kid's a genius, but he's not one of those society-shaking geniuses like Reed Richards who are so common in comics. Peter's more of a specialist - he's largely just a very talented engineer with an additional talent for chemistry. He can whip up a gadget without much trouble, and his web formula is obviously brilliant, but he can't compare to someone like Reed, who is a master of every single scientific field. Pete can't warp reality or build a robot or put together a death ray - his main claim to fame is a really stretchy glue that evaporates after an hour. Sure, he's a hell of a smart guy, and probably one of those people who could startle the world with his intellect if he'd taken the time to go to graduate school and rack up some extra knowledge and a few degrees, but he's never going to do that for the simple reason that Spider-Man would invariably bugger up the process. The reason that he's stayed a 'regular guy' is that all of the inventions he comes up with are specifically intended for himself - most of them aren't in any way useful unless you're Spider-Man. Being Spidey is his main occupation, and this tends to get in the way of scientific advancement.