The preferred spot to watch Wishes is from Main Street or somewhere around the "Hub" (the circular area right in front of the Castle where the other "Lands" are entered.)
The real "SWEET SPOT" is exactly in front of the ICE CREAM shop.
(Don't stand under the umbrella tables, just NEAR them.)
From this spot, the fireworks appear "centered" over the castle (very crowded here, though).
All the area heading up Main Street from there, as far as the PAL MICKEY store, is great viewing as well.
This is where Wishes is DESIGNED to be fully appreciated.
The Castle's front facade (with added lighting and projections) is actually a part of the show.
NOTE: If you go up toward the train station any FARTHER than the PAL MICKEY store... they DON"T turn off the LIGHTS of Main Street in that area. So you'll be viewing with hundreds of lights still in your line-of-sight.
The next-preferred spot is on the bridge between the Hub and Tomorrowland (on the Hub end, not Tomorrowland.)
"Tinkerbell" also flies from the top of the castle over to just above the "Noodle Station" open-air restaurant at one point early in the show.
The reason to see Wishes at least ONCE from one of the "sweet spots" is that there are "front" fireworks (fired from the roofs of Fantasyland) that are best viewed from in front of the castle.
There are "rear" fireworks that are aimed to erupt behind (and centered over) the Castle.
So, if you can withstand the CRUSH of people, and don't mind the longer "in-between" wait time after the parade goes by, the Main Street area is tops for viewing "Wishes".
WARNING: No matter how tempting in may seem... Do NOT stand on the sidewalk between the Hub and Frontierland OR on the sidewalk between the Hub and Adventureland... the (nearly INVISIBLE in the dark) trees BLOCK the main fireworks and the sound is ABSENT/MUFFLED here (by design?).
AND in spite of how good the idea may look before the show, unless you KNOW EXACTLY what you're doing, do not attempt to view Wishes from the Noodle Station seating area.
The main fireworks are hidden from MOST of the seats at this restaurant area and they don't kill the lights or pipe in Wishes' sound here either.
There are PLENTY of other places to see both SpectroMagic and Wishes.
Many here have their favorites.
MY spot is way back in Frontierland by the "Turkey Leg Stand" (we don't eat the legs, but its a great place to view the parade!)
Then, RIGHT after the parade ends, we jog across the "bridge" to Splash Mountain and take a quick ride ("nobody" is in the queue, most folks are still at the parade route).
Then, after the Splash ride, we walk back to the "bridge" from Frontierland and usually get there just in time to see ALL of "Wishes" from there.
The SOUND is supplied back there, and you can see nearly everything (including Tinkerbell).
The things you MISS back there are the fun/beautiful castle-front effects and the symmetry of being in the "center of the stage" for the fireworks.
But the fireworks are HUGE, regardless, and the BIGGEST ones ("rear" fireworks) are actually sent UP from the back of MK, near BTMRR and Splash.
So pick your spot, and enjoy the show.