Bathroom segregation is kind of pretentious anyway. It doesn't work. If it's a guard against perversion, where are homosexual people supposed to go? Cubicles are private enough anyway, all you need is a room of cubicles. Change rooms ought to be full of cubicles to change in anyway because no one really wants to be naked in front of strangers.
I do think there should be some testing of people who want to change their sex though and make sure they're doing it for the right reasons. But someone living full time in one gender should be allowed to have documents marked that way. But it is kind of true that gender/sex is a mostly useless detail.
And in terms of relationships? I like Courage Wolf's advice of "If it's pretty, fuck it, there is no gay". Fair enough not being with someone who you're not attracted to, but if you're a straight guy and you're attracted to something that looks and acts like a girl, minor details don't matter. The autohomophobic idea of liking a transgirl being gay is ridiculous. People who fuck blow-up dolls usually aren't sexually attracted to inflatable objects are they?