Terence, you have indefatigable enthusiasm. The effect it has on people is inspiring.
In the sense of exuberance, but you feel positively about it.
On its own: positive.
Modifying a neutral quality: positive.
However, it's not incorrect to use it as a modifier of a negative quality, so the obviously negative "your indefatigable stupidity continues to amaze me" is a valid use, too.