In my humble opinion, crummy weather at WDW makes for a great trip. Yes, you might not want to do the water rides, but attendance will be lighter, so lines will be short and you can actually spread out and enjoy some quiet times. It's kind of amazing to turn around in Fantasyland and not see any other guests or just walk up to a parade route right when it's starting and have a good spot to stop and watch. Or walk up to a table service restaurant and get seated right away...... Pack a light rain jacket, stuff an extra pair of socks in your backpack every day. Wear quick dry shorts or trousers if you have them and enjoy!