There is another "Sea Screamer" boat, called the "Sea Thriller" located on St. Petes beach.
We have done the Sea Screamer a couple of times and think it is definitely worth the price. The cruise along the millionaires row of gulf side houses is nice and it's quite good when they open it up too. If you see dolphins, it's a great bonus. Make sure you cover your expensive camera equipment, because that salt water spray will more than likely ruin it.
I wouldnt worry about this being harmful to dolphins, infact quite the opposite. Play is a very important part of a dolphins life and they love riding in the wake or the bow waves of boats. I would be more concerned about the dolphins being kept from their natural environment over at Sea World and DC.