I know there has to be more. From the moment I wrote that, I've had a feeling like there is another really good example of a hit coming from slowing something down, and/or making it less intense.
Vanilla Fudge's slow and ponderous version of "You Keep Me Hanging On" comes to mind, but they made it heavy, and the original was a hit... probably a bigger hit.
There is an XM radio station, Coffee Shop, I think. The vast majority of songs on it are low key, down tempo acoustic versions of songs. But I'm not sure any of those versions supersede the originals.