We have not done Wishes, but we will on our next trip. We did do Illuminations and did not like it.
Illuminations offers only bar height tables, no seating. We were there 15-20 minutes before they opened the area and were only 2-3 parties behind in line when they did. There was a crazy rush to get inside and a push to grab the few tables that are at the railing. Even as close to the front as we were, with a toddler with us, the front tables were all grabbed. We wanted the view more than a table, so we ended up sitting on the ground trying to juggle food, drinks and toddler in a pretty dark area. It was not worth the money to us, especially when we don't usually have much trouble getting a nice viewing spot on our own. As far as the food offerings- they were fine, nothing I'd note as exceptional, but there were good. But the desserts really aren't our priority, it's the experience that matters to us.
I have no personal experience with the Wishes buffet, but I know in general, the crowds for Wishes are much pushier and honestly- rude. We've had some bad experiences there, but we want a decent spot to see the show and fireworks so we're going to try the buffet. We're booked under the old price though and that makes a big difference in what we're willing to risk. I'm sure there are others that will post that have had experience with it as I only know what I've read on these boards.