You will be quite able to enjoy "Wishes" at MK from the beach at FW.
You will have a much better viewing-angle if you find a spot on the lake that is much farther RIGHT (as you look towards MK/CR) of the boat-docks.
Ask a CM where the HAY-RIDE stops to view the Water Pageant (BTW, be sure to TAKE a hay-ride while you are in WDW... its low-cost Disney magic!)
Once you get to the clearing, spy the castle and you will be treated to a beautiful fireworks show.
We have also enjoyed Wishes from the PORCH at FW's "Crockett Inn".
Its a bit "through the trees" but most of the explosions are above the tree-tops and sitting and ROCKING in your chair during the show is a nice experience.
BUT... Wishes is an ENTIRELY DIFFERENT show when seen from Main Street INSIDE the MK. So, of course, don't miss THAT.
The "changing" castle facade is a very neat effect, and the spray of vertical pyro "streamers" is much more dramatic when viewed at the "sweet-spot" (anywhere on Main St.) and the music and narration complete the show.