For me, it's not a matter of being mainstream or not, it's a matter of what I find erotic. I did find the rivalry between the two of them (I watched a good portion of this season's TUF, and in the past I was an avid follower of UFC/MMA but not much any more) intriguing, but I don't find fights that can be expected to involve broken noses, shut eyes, or (their first fight) a hyper-extended elbow and a broken arm to be erotic. Not my thing, regardless of its popularity. Even the risk of an injury like Silva's last night (and it's always a risk) is enough to shut down any sexual interest in my part.
As for purely athletic/sporting interest, what I've seen of the UFC's women so far has me at 'meh.' I think they have several years to go before they fill the talent pool for the women. I watched the first Rousey/Tate fight online not long ago, and Tate has no business being in a title match. She's not good enough. (Having said that, I absolutely think that when they do fill the talent pool for the women, they should be watched/discussed/etc. just as much as the men.)