I agree with every reason you threw out there, and I want to add one of my own... Recruiting is crazy now, with the internet and social media, coaches are looking at kids in middle school. There are only so many scholarships at the big name programs, so a lot of that talent drops down to the smaller schools. Also, guys know they'll get at least 3 big games a year playing for a decent "mid-major" football program (one where they get paid to come visit and be a warm-up... hopefully... another in the league championship and probably another in one of the myriad bowl games).
And the fact you brought out about stale tactics from the B1G is true. The spread was a great equalizer and still is. It creates space, plain and simple. A few missed tackles and all of a sudden you're putting up points on the big guys.
That said, though, it still comes down to recruiting. The B1G, for whatever reason (weather, perception, hotness of the local female wildlife) has trouble keeping up in recruiting. Honestly, if you're a big name talent and Sark comes to your door and says "Play in Hollywood!", you're taking that trip, at least for the experience. And who knows, maybe you connect with someone there, and that's it: you're sold.
As far as ways to fix the disparity? I dunno. I've always repeated the "everything is cyclical" drivel, but the B1G is on one heck of a down swoop.