I use Touring Plans, but I agree with Finngirl that you have to understand what goes into creating those numbers to begin with. Touring plans also does well to explain how they get at their numbers, and much of theirs has to do with the ride wait times. However if there are special events going on, that doesn't mean that the Park on't be crowded with guests doing non-ride based things. They have worked very hard over the past several years to adjust their data points to reflect the special events and these things are usually noted on their calendar as Disney has tried to level out it's peaks and valleys to a constant flow of guests.
You also need to know that no matter what the numbers say ahead of time, you never really know what it will be like. It's all just an educated guess.
I prefer to travel in times that Touring Plans says crowds are at a 3-4, but I can be comfortable up to a 5. After that it begins to get a little much for me, but members of my family have anxiety and really don't like dealing with crowds.