My wife is a 'turned in only' sub. And she has to be even more turned on to be a domme. Me I am both Dom and sub every day, although more so when horny. I can usually switch either way given the right partner. However to top me my partner needs to be strong, only one woman has every managed it. My wife does but its more of a game, she still isnt, and may never be at the stage where she demands enough control that I SUB rather than choose to play sub... Its fun nonethless!
Its easy to get bored, do the same thing until it doesnt excite anymore. We vary our play or fantasies over the years. We had a ponyplay phase, lesbian phase, cuckold phase etc (hardcore fantasies and milder play).
One discussion at chastityexperiment talked about wanting to be exposed in a chastity belt. One of my wifes friends knows about it. In fact I once had the fun of massaging her head to toe in her bedwear while I was locked. She said that since I was locked it was safe to ask me to do that. She is very cute and I enjoyed it immensely. Two of my friends know as well, but they are both kinksters, one even used to be a pro-domme. Its not as exciting them knowing, although still some :) I admit though that I would never tell a non-kinkster again without serious thought.