We had tickets to this tour through the Tampa City Pass, we went a bit out into the bay and did see dolphins, some came quite close to the boat.
The tour guide was good at pointing them out and telling about the dolphins, the music on the boat was a bit loud though.
Parking at the marina can be difficult we came early and found a (very expensive) parking space, by the time the boat left, all parking spaces were occupied so come early!
Overall I would recommend to take a boat tour, but don't expect pods of dolphins jumping after the boat, we are visiting them in their natural habitat and they will show if they choose.