I have had the 3DConnexion SpaceNavigator for years. It's useful for cad/3d modeling.
The most use I have actually gotten out of it is in KSP.
I was surprised as hell the day I noticed it working in KSP and it makes working in the VAB a dream. The newer drivers finally allow you to use it as a joystick in unsupported software. This is something 3DConnexion has almost fought against for years, but they finally relented and made the thing useful.
On the other hand the drivers are huge, finicky, and a memory hog and the lack of buttons on and the placement of the only 2 it has actually a substantial hindrance.
Overall, I can't say I have gotten my money out of it. If we were talking about the SpacePilot Pro with the new drivers I would be all over it.
Now for the Leap Motion, it's gimmicky and the store system is crap. That's all I really have to say about that.