Bad news first...none of the restaurants will gaurentee you a table with a view. Some will let you request a table, but they will warn you that it might mean a long wait and you may not be seated until after the show.
For Wishes, I've seen them from Narcoossee's (Grand Floridian) and California Grill (Contemporary). At Narcoossee's, there is an outside veranda that guests can watch the show from. Unfortunately, it means that even if you have a window table, people might end up blocking your view. Over at California Grill, there is an outside observation deck to watch the show from.
This is from Narcoossee's veranda:
This is from California Grill's observation deck:
You can also see some of Wishes from inside CRT, but it's a limited view and not terribly romantic. It was a lot of fun, but it's the type of place you go more for the atmosphere (eating inside the castle!), than the food.
In terms of IllumiNations, the best chance of seeing the show is from Rose & Crown. You may or may not be allowed to wait for outside table. If your table does not have a good view, there is a reserved viewing area for R&C patrons. I like R&C, but it never struck me as terribly "romantic."
I've not eaten at La Hacienda, but I've read that some of the tables have a really good view. Unfortunately there is no viewing area for those at tables without a view.
You might be able to see some of the high fireworks from the Boardwalk, but there aren't any places to see the whole show.
If I were looking for something "romantic", I'd probably go with Narcoossee's or California Grill. I really liked the food at both places, so it's really a matter of your tastes.
One other added "bonus" is that from Narcoossee's (and California Grill) you can also see the Electric Water Pageant.