The experience is worth the money. The boat is nice, and the manta rays are worth it. Just a great experience.
Our guides were Captain Bill and First Mate Tanner. They were both helpful and knowledgeable, and treated us extremely well. Captain Bill had a bit of a 'tude about getting out of the harbor early to get a good spot in the manta area, which would have been ok except it was pretty rough that night (which he knew before we left), so we spent an hour anchored on the boat while it was rocking and rolling - wish I'd have taken Dramamine! When it was time to swim, they were all about our safety and comfort. And, of course, the manta rays were amazing!
When I got sick in the water, Tanner could not have been kinder, more patient, or more helpful. What could have been awful was just business as usual for him, he knew just what to do and so it didn't wreck my trip at all. After that, I went up on the boat a little early and the rays are cool from there, too!
The wetsuits are a must - you get cold - and the snacks are a nice touch. Overall, I'd say if you're include need, do it! And Manta Adventures (at least Captain Bill and Tanner) are delightful and expert.