We went last August 13 – 16. We were actually pleasantly surprised on the crowds. It really wasn’t too bad. Like others have said, summers are nice since the parks are open for the full hours and everything is running at peak capacity and are fully staffed (not to mention AP blackouts).
We are like you; it was about 4 years since our previous visit and so we aren’t necessarily the most park-savvy people there are. We also wanted to see and do as much as possible in the 3 days we were there. Because of that, we opted to use a touring plan. We used RideMax and were very happy with the results. If for no other reason it gave us a plan of attack on which rides to do next. Best $15 we spend on the whole trip.
As instructed by RideMax we got there early and took full advantage of lighter crowds in the morning and used fast passes to their fullest extent. We even had time to walk back to our across-the-street hotel for a nap/swim every afternoon.
Bottom line is that we really liked visiting in the summer and will probably do it again in the future.