It must be a more natural pairing of plain forms and masculinity for guys, though. As a female, my greatest worry is finding that balance between being perceived as feminine and girlish and, well, overly rude or forthright.
Regardless of what the textbooks say, of course I realize women nowadays don't add a lot of わ、って(よ)、かしら 'proper lady' particles to the end of sentences but even how much to leave off だ or add なの, use of ちゃう・じゃう and other contractions, etc。 are nuances I still need to gradually negotiate with myself (and of course my partner, although I'm fairly sure I know he'd prefer a tilt towards the a well-bred woman !).
One area in which I've already made up my mind, however, is refusing to concede to "women's speech" if it seems to have been adopted inappropriately, such as purely to make women sound softer or more pliable (ie the rampant replacement of 上げる for やる)。
As you say, though, Dave, I do feel my personality change when I'm there even to visit and the balance of life spent thinking in Japanese and English will surely be a rather unsightly work in progress for a long while to come.