Is the only way to see things on the island by paying for a tour or can you explore on your own? Renting a golf cart sounded fun...

Would Balboa Island be a better alternative to Catalina?

To answer your last question, first, no, Balboa Island would not be a better alternative -- in my opinion. Balboa Island can be seen and done in 2 hours, and there's not an awful lot to do there other than walk around and eat Balboa Bars. The postage stamp beach that exists is, imo, kind of dirty and the water doesn't look a whole lot better.

Now, onto your first question -- because of the expense of the Catalina Express, you should take the 7:30 p.m. boat back so you can get nearly a full day on the island and get more bang for your buck. Assuming you're going in summer.

Catalina is one of those places that kids run free and have a LOT to do. Lots of places to explore, lots of water adventures, from rafting to kayaking to snorkeling, to even scuba diving if you want to take a lesson. Lots of places exist that rent rafts, blow up tubes, kayaks, etc. Day trippers can use the various bathroom and showers along Crescent Avenue to change into/out of swim suits. Bring a towel. There's also lockers, most notably at Descanso Beach on the other side of the Casino so you don't have to drag your stuff all around.

There's parasailing and a new zipline (the latter of which I haven't tried, but can't wait!); there's the submarine tours that are pretty amazing. There's the Casino tour. There's the very cheap (like $5.00 or so) tour of Avalon. You definitely can explore on foot nearly every inch of Avalon. You can also rent bikes and explore on bike.

Although there's big business in the golf cart rentals, and this seems to be a lot of fun for a lot of people, I have found it to be a needless expense since it really is so easy to get around.

In short, to really see that part of the island around Avalon, and have time to relax and chill, be it on the beach, in the water, or in one of the local watering holes, you need a solid day.

Thought you might be interested in this thread: http://www.fodors.com/community/united-states/worth-going-to-catalina.cfm. Have to say I'm still not sold on a day-trip when we go in a couple weeks.

And I don't necessarily agree that Balboa Island wouldn't be a good alternative. It's true that there's not much to do/see on the island itself, but if you hop on the ferry across to the Peninsula, you'd have a lot more options.

Thanks for all the input! Our plans have worked out such that we are going to take the last boat over, spend the night and return the next day on the 6p. boat. Thanks again!

Just got back today from a 4 day/3 night trip (one night on the Queen Mary and 2 nights in Avalon). You made a good decision --except I'd probably take an earlier ferry over. You won't be over to Catalina in time to do any of the evening things like the flying fish boats etc. and will leave too early the next day to do them.