I think this is exactly how to do it with simming. If you are Florida, decide to sim the Vandy game and they beat you... Well, sorry, but take the loss.
I do a similar thing with my dynasty. If it is a FCS game, or a game against a C or lower team, I usually sim unless it is a recruit visit game. I think this allows for an upset or two to occur that probably wouldn't if I played the game. I don't usually mind the upset because I lose around 1 or 2 games a season playing the game.
Another thing I enjoy (and something that helps combat the endgame of 4-8 undefeated teams) is to play the Duke/Florida State game using the CPU play call and generally laying off the sticks. It's kind of fun to have to throw on a 3-step. I do control the run plays, but the talent gap is such that one needs to be on top of their game to win.
Deckster59 does what I do as well. I have a straight sim dynasty that I use to populate Madden.
That said, I play all "R" games: Rivalry, Recruit (visits) and Ranked. I also play all bowl games (which I am routinely spanked in for some reason).