We attended the Plaza party last Saturday. MK was crazy, so I was very glad we had reserved the dessert party. About 10 minutes before HEA started, a family tried climbing over the back fence to get into the garden viewing area. It was a younger couple with a baby. The mom climbed into the garden first, and then the dad handed the baby over the two fences. I just watched them in awe, hoping security would come over soon. I didn't want to have to complain, but we all spent a lot of money for this party and they knew they weren't supposed to be there. Before the baby was completely over the fence, security was over there telling them they were not allowed to sit in the garden area. The security guard was very polite about it, and even offered his hand to help the woman over the fences. She actually smacked his hand away and was livid. I'm glad they got caught.
For the party we attended this past Saturday, we arrived right at 745 (that is what was on our reservation and in
MDE). The Plaza seating area in the Tomorrowland Terrace was completely full! They had a few extra tables set up by the Terrace viewing party and seated us over there (we even had the fancy table cloths and centerpieces on our table). And we used the Terrace party dessert tables.
There isn't a bad seat in the Plaza Garden viewing area IMHO. I have done it twice this year. The first time, I stood against the front fence and the view was great. We did it again this past weekend, and we chose to stand against the back fence. I definitely preferred the back fence. I could lean, and there was no chance of someone standing directly in front of me and putting their kid on their shoulders right before the show began, which could have been a problem by the front fence.
Personally, I prefer the Plaza Garden viewing. We used to do the Terrace viewing with Wishes, and I didn't mind the slightly off-center fireworks because I had seen Wishes enough that it didn't need to be perfect, but Celebrate the Magic wasn't great from over there. But with HEA, you need to be directly in front of the castle to get the best view.