Yes, definitely don't go to the parks if it's raining. There's NOTHING to do at WDW when it's raining!
I know that it makes it harder to plan and annoying because you're in and out of ponchos, but to let a normal Florida rainstorm spoil your entire vacation is silly. No vacation anywhere is always going to have perfect weather.
Animal Kingdom can be great fun if it's raining -- different animals come out to play, and there's no problem getting wet on Kali River Rapids! All the big shows -- Tarzan, Lion King, etc -- are indoors and will be presented even if it rains (unless we're talking hurricane deluge, which we're not), and probably the only thing that would be cancelled is the parade.
At Epcot, you won't be able to ride Test Track, and some of the live entertainment won't be out on the streets, but otherwise, everything is up and operational in the rain. Even IllumiNations will run in the rain, and the lasers actually look a lot cooler when it's raining.
Get out of the mindset that rain means constant, never-ending, all day rain and into the mindset of how many fewer people will be there and how much fun you'll have jumping in puddles in between attractions. And then enjoy yourself!
