So, there IS a perfect spot for Illuminations as determined by the show designers, however there's a catch. One, it is on the lowest portion near the water right at the front of the lagoon when coming in from Future World. There is a marker in the concrete there designating the best view. This area is roped off and often not opened depending on the wind. They get a yay or nay call about 5 minutes before the showtime and will let people in there if the Fire Marshall says it's okay. Also, this area is now in the FP viewing area, so you have to have an FP to even get a shot at this spot. The regular FP viewing area isn't bad though, but if they let you down to this area there's no beating it!
Note: These policies may have changed since I last experienced them, but it was this way for a while.