1. Rain in Florida typically lasts a short time. It runs heavy for 30mins to an hour or so and then doesn't rain for the rest of the day. At home, people typically wait it out. For instance, I wait for it to stop raining before I go run errands . It's predictable. On your vacation, my suggestion is either go inside ( like go to the land pavilion in Epcot, go shopping, go eat) or to a show like Beauty & Beast in HS. It will end soon.
2. Weather people know ****. Our humidity is so high here they always say it's always going to rain.
3. WDW and Orlando at large is such a big place that it might be raining in one park and clear in another.
4. You'll enjoy that rain when it cools you down.
5. Carry a poncho everyday. I mean it. The one day you don't bring it, it will rain.
6. It typically rains either just in the morning or just the afternoon. Figure out what time of day it will be raining- plan accordingly.
I have lived in Orlando, Tampa, Jacksonville, Pensacola since I was 5.
You're not wasting money. It will be fine. Rain has never ruined my vacation.