We were in a lodge tower room in Sago Cay with a marina view (standard view), but if we looked to the left we could see Space Mountain from our balcony. I would guess that most of the rooms on that front side of Sago could see it. Not the castle though.
I've also heard people saying they could see MK from rooms on the far end of Conch Key on the pool side, that's also standard view.
Although I was unable to see the MK, I could see the fireworks from my gardenview room in Big Pine Key. If you are in room with a view of the quiet pool in Big Pine Key, you would be able to see them. As TigrLvsPooh said, many people also enjoy the marina views.