If you are shooting Wishes at MK, this is what I do. I watch Spectro right outside of Casey's. Then as soon as it is over, and as soon as traffic permits, I immediately move to the center of Main St. (Anywhere between Casey's and where the Tip Board is) and stand there with my tripod. That is the best place to get the fireworks with the Castle directly in the center of the photo's. Now...you will have to be there a good 45-60 minutes before Spectro if you want a front row seat, but the payoff is fantastic. There have been times I just wanted to shoot Wishes, so I got there a lot closer to the start of Spectro, and then just moved to my spot in the middle of Main St.
My favorite place to shoot Illuminations is in the area across from Italy in the WS. Go out and cross over the bridge, and you can get a front row view of Spectro. Sometimes there are private gatherings over there, but even so, I have found great spots. Best part is it is not as crowded as the Future World side of the lagoon, so you do not have to be there as early. I still like to get there around 45 mins prior, especially if I have plans to shoot Illuminations. I want to be sure I get a front row to set up my tripod.