Platinum Package doesn't even seem worth it if you want to spend a lot of time at the parks because you won't even get to do all the things the Platinum Package offers. If you want to do a few of them, it'd probably be cheaper to pay OOP.
You can price out what you want to do now and estimate prices since they usually don't change that much.
For example, FI and I sat down and decided we wanted to stay at AKL Cl with the dining plan. We were going to upgrade whatever tickets we bought with the package to annual passes. I looked up the prices of those for 08 when we started looking and just added on an extra couple hundred dollars to be safe. Then I went through and decided what tours and extras we wanted to do (Keys to the Kingdom Tour, Sunrise Safari, etc). Then I had some idea what it would cost.
It was nice because Disney came out with the Buy 4 Get 3 sale which saved us almost $1600. And we get discounts on tours and other things like mini golf, with
AAA, APs, or Disney Visa. I didn't factor any of that in because I'd rather be too high then too low.
Then I knew where we were at (a lot of money

) and knew about how much it would cost.