Wishes is being replaced soon (in May?) with a new nighttime show. Not sure if you knew that, since "Wishes" is in your title.
Anyway--it rained terribly the night of our Wishes plaza viewing party. We were led to the garden area in a drizzle and then the rain worsened. it was announced that fireworks were on hold temporarily until the rain let up. I am not sure if we would've been allowed back in the dessert area. We went to buy Disney ponchos (our dollar store ones didn't cut it!). Soon after the rain let up some but it sprinkled on us throughout the show.