My wife and I have put in about 1.5 - 2 hours there 2 or four trips each of our last three trips. We started going on the boats just to learn the places to go. We have our own gear and turned to guiding ourselves now. I recommend putting in at Catalina Cove, and swimming north about half way to Arashi and then drifting back Down to Boca Catalina. There is tons to see if you are patient. The comment about the Starfish is spot on! Look for Pelicans and other birds to find the bigger schools.
We have been disappointed with Baby Beach the past two May trips. strong current, lots of sand being stirred up, and little chance to see much.
Mango Halto sound great. We have spent some time on the reefs their either at De Palm or charter boats, but never found the beach. Now with Wikimapia there is no way to miss it. I have spent much of my spare time in the plast week studying the island as this May will be our first 3 week trip. We will lots of spare to to explore more than usual.