With the opening of CarsLand the best plan may be different than expected. In the past I would usually plan on going to DL on the lower attendance day but this year DCA may be the busier park, so that one might be the one to attend on the lower attendance day. This year you might want to plan as late as possible, so data can be collected on how CarsLand is impacting attendance. I think planning 2 weeks in advance is more than enough if you know what you're doing. If you don't, I would suggest getting educated, so when the time comes, you can use your newly gained insight to come up with your plan.
When are you going to be here? If I wasn't an AP who goes all the time, I would definitely plan each day in the park. I'm always baffled by tourists who come for 1-2 days and enter the park, after paying a small fortune to get in, and haven't a clue what to do. It's an incredible waste of time/money to stand there at the entrance with a map in your hand and ask your group, "So what do you want to do first?" Ridemax is a great program to create a customized plan, but there's lots of other basic touring plans if your needs are general. Google
Disneyland touring plans and you'll get a bunch of resources.