I'm a Michigan grad myself, but I think it's a close call for Michigan State. I'm pretty sure it used to be a 5-star system, and in that case, I think you'd have to call them a 3*. On a 6-star system, they're probably a 4* after a good year and a 3* after a bad one. Even if the Big Ten isn't the best conference, it's still one of the power conferences, which guarantees at least some high profile competition. They've also had some memorable wins over Notre Dame in their non-conference schedule in recent history, and they've produced a fair amount of NFL talent.
Could go either way. (By the way, I'd also be fine with Michigan being only a 5* after the year we had!)