We go every July (used to be just DH & I, but this July we'll have the baby with us!), and we've never made PS's before. Now we have never eaten at Sci-Fi or Liberty Tree Tavern before (I have allergies/food sensitivities, so it's because of food selection), but we always eat at Garden Grill/Epcot, Ohana's for breakfast and Marakkesh for lunch. We eat earlier rather than later, and there has been only 2 of us, so perhaps that has made a difference, but the past 3 years, we have found July not to be busy at all!
That being said, it wouldn't hurt to make a few PS's as others have said, just in case as it depends on many things as to if you have to wait to eat or not: how many in party, time of day, time of year, how popular restaurant is and now to consider: the AP purchase of the DDE card. This certainly means that table service restaurants are going to be a tad more busy than usual - especially the character meals I'm sure! So for this reason, PS's would be more important than usual I would imagine!
This year, being that we have the baby, I've made PS's for our March trip, and will be making some for our July trip as she eats lunch & dinner early, as well as for the DDE discount reason mentioned above.
Have fun and happy eating! Tiger aka Piglet's Momma