I base my irrelevant opinion on a couple of factors.
1. NDSU and SDSU won’t stick around for long. UND and USD might not either.
2. There are really only four to six teams who can win the natty every year anymore. 6 is probably pushing it. All the decent east coast teams are gone. App State, Georgia Southern, James Madison. Sam Houston left as well. I know that I am missing other teams who moved up. Idaho is the only one I can think of who dropped back down. You take the Dakota’s out of the equation and we are left with absolute garbage.
3. The fan base isn’t going to watch B league football. Last night’s game was an example of a complacent fan base. (Not blaming all the bad fans. Yes, Turkey Day weekend was a factor).
4. I think there will be an FBS mid tier playoff at some point. I hate the bowl games, but hopefully that changes. Better competition and the Griz have a stadium and facilities that accommodate the move up. Hard to believe this, but Boise State is probably going to make the 12 team FBS playoff. Looks like #11 right now.
5. To answer your question about FCS compared to FBS point spreads. I don’t think there has been a major shift in those numbers. I don’t put a lot of stock in those numbers. Usually the first game of the year or second. I think it would be better to look a the top tier FCS teams and make the comparison. All it would show if those FCS teams could probably be competitive by moving up.