sea world can get pretty busy too.
It might be "fewer people" than say disney, but the park is a lot smaller. So it holds fewer people. I went right around christmas time, on like the 29th. Of course they were doing the polar express for the wild artic, but all day the line was 60min or more. And after a shamu show dump, it went up to like 90mins. Manta was just crazy long, the line was out the entry. I even had to wait like 20mins to get on the sky tower, and they were using both levels. Even to get into the sharks, there was like a 15 min line out the door. Because they can only let so many people in the building... so every few mins they'd let another 10-20 people in.
Of course being cold outside, it was a great chance to sit up close at the shows... but the rest of the stadiums filled fast.
Summer time Aquatica would close by 11-12 to capacity, but usually by 3pm they'd re-open. Depending on the hours. It's just as easy to go in the afternoon, the sun is less brutal, the crowds are a bit less, and you can still accomplish everything.
Last summer I would go once or twice a week to aquatica, but always in the afternoon, and I could do anything I wanted over and over again. Of course the hardest part of there being no line is climbing the 10 flights of stairs to the top of the slides. At least when there's a line, you get to "slowly" walk up those steps. It took a couple weeks before I stopped getting winded at the top of the racers.
If you're doing busch gardens and you love the thrill rides, it might be worth the added cost for the quick queu. I don't think it's worth the price for Sea World.