Disney's California Adventure is not doing at all as well as Disney would have liked, or expected, for that matter. Part of that might be because DCA did not open during peak season. Instead, it opened in February, when attendance numbers are usually down from summer season.
Also, Disneyland has over the last few years lost a fair portion of it's foreign market, with Tokyo Disneyland regularly posting the highest attendance numbers of all the parks. Also, DCA was not highly publicised, at least here in the East Coast market. So unless you get the Disney Channel, read Disney Magazine or any other Disney-published magazine, there was no way to know (easily) about DCA. Okay, there is one commercial for DCA with Buzz Lightyear snooping over Disneyland's hedge, but that's it, and I don't see it regularly enough to make me believe that it's a big publicity run.
All in all, DCA may do a lot better over the summer, so I guess we'll just have to wait and see.