I've done the dine only (several times) and I highly recommend it! It's a great way to get a decent amount of time in close proximity, and see the orcas doing something other than just the show behaviors. The trainers will answer questions.
The earlier you book, the better your seats. All the seats are close but the best ones are literally up to the glass.
It's not great for photo opp with the orcas though. If that's your main goal, you'd need the up close tour.
The price is also wildly different. The Dine with Orcas includes a full meal & non-alcoholic beverage which makes the whole thing a decent deal as far as SW food goes.