The thing with American remakes of British Shows in general is that British TV can go farther than American shows because of the censorship levels.
I direct you to the remake of the British comedy Coupling. It was a hit in Britain because it went far with talks of sex and relationships. America tried to literally import the show word for word by reshooting the scripts with american actors. And it failed, horribly. lasted about 2 episodes. Why? because in order to bring the scripts over, they had to alter not just some of the words because of dialect differences, but also because of censorship. The conversations just could not be shown on NBC at 8:30.
BBC America is even under constraints when it comes to shows having to edit content for Amercian censorship rules.
Torchwood is a dark and gritty show which is why I like it so much. It pushes the envelope on violence and sexuality.,While those type of things are not unusual on shows like Nip/Tuck and Rescue Me, those shows are on FX after 10 pm where they can show more. Fox airs programs pre 10 pm and have to keep things less controversial.
My biggest fear is that if they were to simply remake the series rather than make it a spin-off, the scripts would have to be toned down. While the aliens and fighting may be retained, the true nature of the series, the character development and relationships would just not pass censorship. Jacks morally and sexually ambiguity would be toned down, his loving relationship with Ianto (something that is just too important to the series) would be reduced to maybe flirting or allusions rather than expression. Even though sexuality is not the basis for Torchwood, my fear is that things like Ianto and Jack would just be watered down to the point where their love is not shown to the same effect it was. What we would end up with is a watered down Torchwood.
So, I would watch a Torchwood US but would still feel that Torchwood UK is the real deal. If they really want to keep the darkness and the lessons, then go for another network like FX which has no Sci-Fi series and is close to losing Nip/Tuck and Rescue Me as they are in their last seasons. Even if this turns out to be a spin-off and another branch of Torchwood, If they want to really keep the tone of the original, then they have to have the show on a network that can push things far.