This is hard to figure out since you would want to go the last week of September in order to get the Value Season rate. I believe it switched from Value to Regular on Sept. 28th this year. Note that when the Value season ends,
Free Dining does as well, so that's something else to think about (they haven't offered deals for Oct yet).
MNSSHP is happening the last week of September, but unless dates are out yet, you might want to hold off on booking to make sure your dates are covered. I was there the last full week of September last year and the final 2 nights of our stay turned into Regular rate. All Holloween events were happening by then.
Hope this helps a little!