You know.. I think this is a hard one, but I think that I have a equation that may help.
RC Heli == Expensive == Has Money
Has Money/Nerd Factor = sexness.
Just as a note, you guys are REALLY showing your age right now. Video games ARE sexy to the younger crowd, as are gamers. Gaming is definatly not strictly a guy thing at all any longer. As for Geeks.. well, they have actually be come sexy now as well. NERDs are not sexy. Geeks are nerds with social skills.
So, I would say that if you're into RC Helis AND have a life outside of the hobby, then it is sexy. If you're unable to have a conversation without bringing up your latest auto or mentioning the latest tweak you did to the pitch/throttle curves... NOT sexy.
As for saying that you need to fly in order to appreciate it.. I hate to break it to you but likly this will always be a male dominated hobby simply due to the differences in spacial imaging between the sexes. There will always be exceptions, but in general, men have an easier time imagining a object moving in a 3d space. Not saying that a girl can't be just as good of a pilot as a guy, but IN GENERAL, from the studies that have been done so far on the subject, this seems to hold true.
unspelling the world one misprint at a time.