My wife only plays alone, always has. She feels that a 3-some or even just me watching would be too "pornographic" (her words). Plus, the men she is with would not likely go for it anyway. They like to think she is just cheating on me with them. This helps in another way too, in that it encourages them to keep their mouths shut.
With my ex-wife, I was present, and that is definitely hot. I would love to watch my wife fucking, but I'm content with the way things are. TBH, it is way more intense, and in the final analysis, I have to say I like it better.