Over 5 years though, I would wonder if you aren't seeing the outcome of a million and one web sites telling everyone that December (barring the end of the month) and January are the best times to go.
Exactly this! When we first started taking our kids to WDW in 2002, I bought guide books because I knew that it would be a much different trip than just DH and I, and my kids were pretty little. I figured I would need advice!
Anyway, every guide book (Unofficial, WDW with Kids, Passporters, etc.) ALL reccomended early Dec as the absolute best time to go. We actually changed our original plans to go in early November because of these reccomendations. For the next 4 years we did early Dec trips (2002-2005). I can tell you that from our point of view the crowds got bigger and bigger every year, or at least it seemed that way to us. WE even talked to people who said that they chose this time because of the guide books. There was no free dining any of these trips in December.
Anyway, in 2006 we went in mid-October and the crowds were so much smaller it was amazing. I mean, a lot smaller! I would go back to WDW that time of the year in a second!
We started going mid to late May because of my sons football season. We could just no longer do October. Also, because our school year ends in mid June, the kids were missing very little learning in May. DH and I both felt the crowds were smaller in May than the 1st 2 weeks of December.
This year we are going late May into early June because of my sons lacrosse schedule. It just so happens to be a free dining period and I'm a little worried about the crowds, but it's the only time we can go. Just have to hope for the best, I guess.
I still miss the Christmas decorations, lights, extras that come along with the Christmas season. Maybe someday we'll go back in early December.