I know that it's almost impossible to get accurate figures, but could the increase in tourism also be affecting the wait times? I have found the parks to be more crowded, in general, now than they were 10 years ago. There was a drop in attendance immediately post 9/11, but it appeared (to me) that things were getting busier prior to that.
I base this on difficulty getting a room, decrease in "special" deals for passholders, etc. And lately, the dining plans have really increased attendance.
So I think it may be difficult to gauge. I just know that in my experience, prior to the last couple of years, FP made things better for me, without making the standby lines (which I also had to stand in during the day) intolerable.
The only way to really tell would be to eliminate the FP completely for a few weeks, and then measure the actual wait time on attractions without it.