I traveled on a sold out sailing of the Dream with my dd, 6, and her godfather. We attended all events, etc. Other than the terminal and the midship elevators, I honestly didn't notice a huge difference in the sold out sailings on the Wonder that I have been on. We did go to the sail-a-way party and for the first pirate party we watched from the deck above, right above the state and had a fabulous view. We watched the fireworks from Currents after the bartender that we befriended told us that this was the area that the fireworks were shot off from and had the best view (and fewest people) on the ship. We couldn't have been more pleased and actually had a place to sit without people blocking our view
The only pool that we ever went to was the family and kid's pool and Nemo's Reef area and never encountered issues. The adult pool was dead every time we walked by, and we passed through often since our room was on deck 10 forward. The Aquaduck was about a 30 minute wait, but we were totally prepared for the wait due to the newness of it. The same was true of
Castaway Cay. We had no problems finding seats on the family beach and the same was true of Serenity Bay. In fact, SB was surprisingly fairly dead, much to our surprise.
All in all, I think it comes down to a persons expectations going into the cruise. No matter how packed the cruise is, it will never, IMO, be as bad as a semi-busy day at WDW (and I've been over 40 times). I'll take a crowded ship any day!