Got to agree with everyone here, all of these choices were baffling.
Demolition was so over at the time, the turn was so quick, it didn't do anything for them. Though, the WWF did need a top heel tag team, especially after the addition of LOD and the end of the Colossal Connection, Brain Busters and Powers of Pain. But they should have dragged it out a little longer. A demolition vs LOD match at WM7 would have been ideal after a slow build.
WCW turning Sting in 1999 was just plain stupid, the fans did not want to boo Sting, turning him heel didn't do anything for him or WCW. As was evident that they had to turn him back face a few months later.
Same with WCW, in 2000, the only thing that WCW really had going for them was Goldberg. A lot of the top stars were not there as much and Goldberg was the only real big/popular star they had. They should have followed WWF's lead and made him the Austin to Bischoff and Russo's version of McMahon.
I would also add Bret Hart's many heel to face back to heel turns in WCW, it did nothing for his character and did nothing for any of the storylines. After awhile even fans of his got tired of it. It just seemed like the WCW writers always wanted someone to turn on someone each night and the only one they thought could do it was Bret.
Dusty Rhodes joining the NWO also comes to mind. It may have been good but after a few months they just dropped the angle all together.
Curt Henning joining the NWO, although it wasn't a bad choice, it didn't do anything for him. He would have faired much better being in the 4 Horsemen group, he would have been more valuable there instead of just being another guy of no consequence in the NWO.
Tatanka in 1994. Though it wasn't bad, it didn't do anything for him and a year later he was pretty much out of the company. They really should have turned Luger heel here and made him more like his Narcissist/Total Package character. I think a heel Luger at this time would have been better for the company than Tatanka. The USA Luger character had worn thin, him going back to heel, he could have been the guy to take the WWF title off of Bret Hart at Survivor Series 94 and dropped it to Diesel at RR95 or WM11.
