I never got the impression from Reed, as presented on Enterprise, that he was gay, nor do I think it was ever intended by the writers to make him gay. Anyone who thinks this, in my opinion, is reading into something a little too much, or simply wants the character to be gay for whatever reason, and are seeing what they want to see.
That said, I think it could have been an interesting plot twist, to reveal Reed was gay. Reed stating he had girlfriends in the past doesn't necessarily contradict that, either, as it could be explained as something he tried, and maybe didn't like it and took a while to realize it.
The only thing I think might be seen as a potential negative is that Reed was always portrayed as kind of uptight and seemed to have such an exaggerated sense of self-reproach and inadequacy. That could be misconstrued as he is ashamed to be gay, as well as something he feels he should hide from his crew mates.
I mean I know Enterprise is 100 years before TOS, but even then, that is an age where humanity is and should be progressive and enlightened enough to not care if Reed is gay or not, and the way Reed was written, I get the impression his character would be obsessed with keeping his homosexuality a secret and be afraid of revealing it to anyone. And to me Reed being overly concerned and constantly worrying what his crew members think of him being gay in the 22nd century is sort of out of character for that era, and makes Reed look basically like he is neurotic, and not well adjusted. Just not a good example of a gay character...one who is self doubting and feels guilty for being gay, in a society that should be enlightened enough by the 22nd century to not care he is gay.
Now, if there were to be an LGBT character in Star Trek, if they are gay or lesbian, it should be portrayed like its no big deal, and no one on Earth or in Starfleet thinks its a big deal. That precedent was sort of set by Dax already. Maybe a gay or lesbian first officer or something like that.
Another idea I think may be interesting is what if there were a transsexual Vulcan? Now, unlike Earth or Starfleet in 22, 23, or the 24th centuries, where LGBT shouldn't be a big deal, I can see Vulcans, who are uber conservative and uber repressed, maybe having an issue with a transsexual Vulcan. Not unlike the shame T'pol had to face for being with a telepathic Vulcan, maybe Vulcan society struggles with the "logic" of a Vulcan who changes his or her gender, and lives as the opposite gender of their birth. I think that would be an interesting story line.