Kind of a dumb question but one of the places I fish I can get usually 3-5 fish an outing, but there's a small two week window in the Spring where it just blows up and I can catch like 25-30 fish where they'll bite anything.  And then for a short widow before that blow up, I get better than average numbers and the fish are larger than usual, they look like fat belly females.  Is that 25-30 fish window considered the "spawn" period where males are aggressively defending nests and will attack anything nearby, and is the period before that the "pre-spawn" where females are fattening up?

Most likely that's the prespawn. 

Not a dumb question....and it sounds like a blast!

I'd agree that you're probably witnessing the peak of prespawn feeding. What I'd do next you notice this happening is find a way to take note of the primary conditions like water temp, weather (like air temp and atmosphere,) water color, and possibly barometric pressure if you can. There is a combination of these that you'll be able to peg down as the root cause of these fish moving up to feed like this. 

Would love to see pics of this wonderful madness after an outing!