I have been on Labor Day weekend, both using and not using the plan. It's very hot and humid. Usually rains a bit once a day.
The parks were not bad on that weekend (MK was pretty dead ON Labor Day last year, walked onto several rides) but the restaurants are FULL. Get TS reservations for sure.
I'll be going down to WDW this Labor Day, but not getting the dining plan. I want a couple of TS meals and will make reservations for them.