I definitely see where you're coming from. Truth be told, I was shocked how well my poorly-sung vocals turned out with a little processing so looks like I went overboard. I already tweaked it so the "aaaah" samples themselves are half as loud and you're right: it sounds a lot better.
I think the best way to reduce repetition is to take the vocals out of the middle portion and come up with another way to keep it varied there. Maybe I'll adjust the flute melody there. Maybe add some harmony, which can carry over into the final portion.