Both of my sons are in wheelchairs and we went to WDW last month. Honestly, it really doesn't matter much as the fireworks are so high, you have to look over people's heads anyway. They could see fine from Main St.
Other suggestions would be the hotels, GF, CR, etc. the music is piped in and there are usually not many people around, especially at GF. An awesome spot is on the ferry dock at TTC or better yet, catch the ferry right as the fireworks are starting and the ferry is going to MK or back to the TTC. Roll right up to the front, or back, whichever way you are going and you can watch the whole thing. Often the captains narrate, too.