My wife and I really enjoyed following your trip report, and now that you're going to Disneyland we had to chime in. We live in Southern California and got married at the Grand Californian in 2007, then took our first trip to WDW together. This September we finally get to go back, and reading your trip report gave us so many things for our must do list. It seems we have similar tastes in Disney fun.
So, back to tips for Disneyland. We talked about it, and the first one we came up with was dining at the resort hotels. In particular we love to visit the quick service snack bar Whitewater Snacks at the Grand Californian. It is usually nice and quiet, and the beef nachos are excellent. Storytellers is the sit down restaurant at the Grand Californian, and they have a buffet with the world's best corn chowder. Seriously, it is very good.
Another thing we thought of was the inevitable comparison between WDW and DL that you'll be making. We experienced it the other way around, but I am sure some of the feelings will be similar. At first the differences will really stand out, and comparing MK to DL things will just seem to be in the wrong spot! Because of this we ended up not spending as much time in MK as we thought we would, but we got over it. DL is so small compared to MK, but it is amazingly efficient. It feels big for being small, if that makes any sense, but you'll just have to see it for yourselves.
We really enjoyed seeing the parks that were totally unique to WDW, so I bet you guys will enjoy a lot of California Adventure. The new Cars Land is amazing and totally worth checking out, even though it will be pretty busy. You have to see the view from the far entrance to it near Radiator Springs Racers, where it feels like you walk into the movie. They also rebuilt the entrance to California Adventure, and a new favorite place to eat for us is the Fiddler, Fifer & Practical Café, which is the coffee shop at the end of Buena Vista street (the main street as you walk in). The roast beef and cheese sandwich is great, and the seating area is really big, so it is easy to get a spot.
For rides, Radiator Springs Racers is the new hit, and while similar to Test Track there are a lot of differences. California Screamin is a very nice magnetic launch roller coaster and a must do, and so is the classic Matterhorn which has just re-opened from a refurbishment. You mentioned Haunted Mansion, and the NBC version is cool to see. Also, the "stretching room" is done with an elevator in CA, which is cool.
One last major difference is that in California, everything is so close. It is totally feasable to walk between parks and have fastpasses at each. Downtown Disney (although way smaller than the Florida version) is right between the two parks, so everything is super close. Walking out to your nearby hotel shouldn't be bad either, and compared to WDW it will be amazingly close to the parks.
You guys are going to have a great time, and with three days of park hoppers and staying close you will get to cover it well. Enjoy! We can't wait for the trip report.