I have been to DC many times, the first to swim with the dolphins, the other dozen times to just chill and drink beer.
The dolphin swim can be taken many ways as you have read. You are in a large group of between 8-12 people and it's designed for you to have a SeaWorld camera take your picture at several times with the dolphin. You can't take pictures yourself in the dolphin pools. You get to "swim" with the dolphin for about 30 seconds for a total of 20-25 yards. The rest of the time you're watching everyone else in your group do the same interactions that you did. The trainers do seem to spend more time with young children than adults (my opinion). Some people love the adventure, others, not so much.
DC has recently opened their new reef with a new underwater adventure which is getting a lot of rave reviews. It's an add on cost as well, but you actually walk on the bottom and get an up close and "personal" view of marine life at the bottom. You wear special helmets that provide air and communication. It lasts for about 45 minutes I've read.
Other than those two things, DC is awesome. You honestly forget you're in the tourist area of Otown while there. It's all inclusive food, snacks, and beer (though it's Anheiser Busch crappy beer) and a few mixed/frozen drinks. The reef alone is where I usually spend several hours a day just swimming with all the animals. It's really fun.
They do only allow 1,000 people in a day, if it's not the week before or after Christmas, there won't even be 500 people during the week, so it's not like being in the hustle of a theme park.
As for the ticket into Busch Gardens or SeaWorld, it's a good deal in that you don't have to shell out more money to get in another park! It all depends on what type of park you want to go to. If you want to see more marine life with a few attractions, go see Shamu. If you want more thrills with great animal exhibits and the newest coaster in town, head down I4 to Busch Gardens which honestly takes about 75-90 minutes to get to from the theme park area.
I hope this helps. If you decide to go, have fun!