Bring them.
Yes it can rain, well no pour. I have used them in the summer & was thankful I did.
Our last trip it poured on our first morning but luckily we were at the MK so the rides were close to one another so we didn't poncho it (but we covered the stroller with it).
On our last day we were on the monorail on the way to EPCOT & the cloud we saw ended up being pouring rain that didn't stop. We walked, well ran from the monorail station to The Land, ate there & then waited a bit but the rain never stopped. We were so lucky to have them this way we wouldn't be soaked.
And believe me these quick showers will cool you off but they will leave you soaked & your clothes will not dry if it is later in the evening & do you really want to sit in an air-conditioned ride soaked to the bone?
Oh & I am going the same exact dates as you, but I am staying at the Poly, my plane arrives around 2:30 & we have PS at Chef Mickey's for 5.
And the next morning we will be eating with Cindy at 8:15 & I am still trying to figure out if I should make PS for the Crystal Palace for Sunday or Monday.