Personally, if I'm staying on Catalina, I don't feel the need for a boat. I can get many more dives in, for way less money, right from the stairs at Casino Point. You can do as many dives as your NDL allows. Fills are easy - there's a fill station just a few steps from the stairs. And the dive park is truly an awesome representation of the best of SoCal diving - gorgeous kelp forests, abundant sea life (since divers generally don't hunt there, the marine life is plentiful) and even a couple wrecks within easy reach.
Of course this is assuming you have a dive buddy with you...if you don't, then that puts a different spin on things. You could always hire a private DM, if you're not into solo diving.
Also, I think it's important to ask if you've done SoCal diving before. Have you? If not, there are some important things to note:
1. This is cold water diving. If you're diving wet, you will want a full 7-mil suit, hood, gloves. Drysuits are common around here.
2. If you're used to tropical diving, you may find that the visibility is way less than you're used to. It can get very murky around here. I'm perfectly happy with 10-15 ft of vis, and it's often better than that - but it's often worse too. Just be prepared.
3. If you do go on a boat, dive boats out here don't operate like dive boats in other popular dive locations. Here, you are on your own. You are expected to handle your own gear, bring your own buddy, plan your own dive, execute your dive on your own and get yourself back to the boat. SoCal dive boats don't dive in DM-led groups - in fact the DM usually doesn't even get in the water, except in an emergency. This can be startling to people who are used to resort-style diving.
4. If you haven't dived kelp before, it's worth reading up on it. Just google "kelp diving" - there are some excellent resources that you should read. Too often, divers from out-of-town have no idea what to expect, and there have been some sad incidents that could have been avoided had the diver done his/her homework on the unique characteristics of kelp diving.
These are reminders that I always like to bring to the attention of out-of-towners. Just some food for thought to make your trip out here better!