Best dates to visit Disney World and Typhoon Lagoon

Maybe a cast member or has been one can answer this..Does anyone know when the least crowded days (i.e. month/days) to visit WDW ?? By this I mean at least a week with very very low park attendance. I have been numerous different times and I do have annual passes.I was thinking about staying on grounds at a Value resort to save rental car and take advantage of additional park hours. Does anyone also know how to get some upgrades for resorts during this offtime?? Thanks in advance for replies.

Late fall (late oct and early dec) are always the least crowded.....and if you go in oct it will still be warm enough for water parks..Hotels are generally cheaper then too
I never notice a big difference between days of the week
Keep in mind that it is never completely uncrowded at Disney World