Treat your FPPs like any other day. It may be a "low crowd" day, but the "headliners" still will build a line and FPPs will help shorten that.
I eat very little QS at WDW so I'm sure that others can provide more input. Here's my run-down of some highs and lows of ones that I have tried
BOG - average food, beautiful location
Casey's - not bad for a hot dog on the run
Pecos Bill's (old menu) - over-cooked hockey puck burger that can be disguised with toppings
Cosmic Ray's - Mall food court quality, but wider selection than most QS in MK
Sleepy Hollow - ice cream cookie sandwich is OMG good and big enough for at least 2 people
Gaston's - cinnamon roll is my favorite MK breakfast
Yorkshire Fish and Chips and Tangerine Cafe - excellent; I like them better than their TS counterparts.
Katsura and Sommerfest - both also very good
Lotus Flower and La Cantina - barely up to mall food court standards. La Cantina is OK for a basic margarita.
Kringla and Les Halles are both excellent for a pastry or snack, I've never tried their other food.
Electric Umbrella - Horrid 20 years ago, with all of the other options, have never wanted to go back.
Sunshine Seasons - Very large variety of generally good food with better than average "healthy" options. Good for a breakfast stop, but by lunch I'm in WS and not looking back.
Kusafari - good breakfast pastries
Yac and Yeti (QS) - not bad Chinese take-out; better than Lotus Blossom
Flame Tree - Generous portions of well-prepared BBQ.
Pizza Planet (now Pizzarizzo's) - Pizza Hut quality pizza. Not great, but better than most DHS QS options.
ABC Commissary - has the distinction of the single worst meal I've had on a Disney property. That was many years ago; perhaps it's gotten better.
Min and Bill's - Tasty hot dog as a grab-and-go
The other QSs - I've tried them all over the years and they all blend into an undistinguished mire of mediocrity in my mind.