That would be a fun trip... Here are a couple of potential issues:
1: Moorings in Avalon are assigned on a first come, first served basis. Normally in the fall you shouldn't have a problem getting a mooring, but I have heard that moorings get sold out early in the week when the Jazz festival is going on. A lot of boats will show up to the island on Wed or Thurs and spend the weekend there. If you show up on Sat, you could be SOL as far as getting a mooring.
2: Unless it's a last minute booking, most (all?) hotels will require a two-night minimum stay on the weekends in Avalon.
If you have flexible plans, you could head over there on Sat and hope to get a mooring. If you get a mooring, you could check around for an open hotel room for Sat night and book it. If you are either not able to get a mooring or not able to find a hotel, hang out for awhile and then cruise back over to the coast.
Also, I heard a rumor that SCOPE might be putting together an overnight/rally around the island trip to Catalina in Oct after the Jazz Festival is over...