Even at Kona, which has always had relatively quick service for us, I don't see how you would get back to Epcot to see Illuminations.
Assume an hour for dinner (and that's optimistic, probably, given a 7:35 reservation - depends on how backed up they might be) and it's already 8:35. Either the monorail to the TTC or walking from the Poly to the TTC is going to take a minimum of 10 minutes (walking). Now it's 8:45, 10-15 minutes to get to Epcot, debark the monorail, enter the park, etc. I'm guessing you would end up seeing Illuminations from the monorail as you're entering the park in the best case scenario.