We stayed there during Columbus Week last year. It was more crowded than I expected after Columbus Day, I thought everyone would go home after monday, (well, not everyone lol). Nope, due to the fall breaks there was almost as many people still there. It was managable, but we picked that time to avoid crowds, yet still go to MNSSHP. In the fure, if I was looking to go during a slow time, I wouldn't pick October. But I won't avoid it either, since I loved MNSSHP and the crowds weren't as bad as summer (or the 2 biggest weeks, Christmas-NewYear's and Easter).
Have fun!
Lori