
Whatever you do don't go do indoor entertainment as it'll be packed. We decided to Disneyquest on a rainy day once, never again!
Just wanted to say, 90% of the guests start to scatter for what they read was a good park in the rain. Basically it makes the parks that peopel told them is bad to be very low crowd and amazing in the rain. you just need to consider what you want to ride if it's going ot be more than a quick afternoon rain as outdoor rides might close and will close for lightning (and coasters in the rain is not fun, the rain stings when hitting you).
I'm not sure a lot of them are going to other parks (unless the better park is DHS). We've been in the 3 other parks during the rain and all of them cleared out and had walk on attractions during the rain and for a while afterwards. I think people head for home or their resort or somewhere else dry.