It's odd, but I just got back from a Thur-Sun trip and the crowds were high, but I was able to accomplish everything I wanted. We rope dropped Peter Pan and basically walked on Tea Cups, Dumbo, King Aruther Carrousel, Mr. Toads, and then took our 6 year old to play in Toon Town. We had such a wonderful morning that it set the tone for the rest of the day. My son never felt let down while in the park which was important for me.
The only "downer" times were when we'd be in line and a ride would go down. Or we'd be walking to a ride and when we got there it was down. Or we'd be on a ride and it'd stop and we got walked off because it went down. Or when we left one park because the rides were down and then went to the other one for a certain ride and when we got there it had broken down. I'm sure the crowds led to them breaking down, but all the people didn't "effect" us so much. It was still Disney. We had a great time.
The last day (Sunday) went like this:
Rope Drop Radiator Spring Racers. Walked to Disney Junior Dance party but the first showing was canceled with a "maybe" for the second showing. Walked to Web Slingers but it was broken down. Walked to the Redwood Creek challenge trail and my son ran around for a bit and met Chip and later Dale. Went back to see Mickey's philharmagic, ate a hot dog while we stood in line for the second showing of the dance party and my son had a blast. After we got out, Web Slingers was finally open as I was consantly checking so the line was short. After, we went back to the hotel and relaxed and recharged.
So while there were a lot of people, we never once thought it detracted from any event. Have a plan for breakdowns and you'll have a wonderful time!