They probably figured, with the popularity of New Voyages, that young(er) Kirk & Spock is exactly what everyone wants to see.
Personally I'm neutral on the issue as long as the story is good - which I'm somewhat sceptical about (if it's really Romulans go back in time to kill young Kirk, old Nimoy Spock follows them?), but we'll see.
That trailer sucked, by the way.
What they need to do is reset the Star Trek universe; make a re-imagining like BSG and Batman Begins.
Not sure about the "re-imagining" bit... it works well for the two examples you mention, but I'm not sure going back to the premise and tossing out the past 40 years of Star Trek and start from scratch will work well. In a way I suppose I'd consider TNG as a sortof re-imagined Star Trek and I think they did it properly then. On the other hand, if it's Star Trek without some of the goofy dated 60's special effects and look-and-feel, I'll be fine with it. We'll see.
As for Enterprise (I liked it ok enough), there's some very good episodes but many more where I just thought "meh, done better in <some TNG/Voyager/DS9 episode>". Series 1 was ok-ish, but the Temporal Cold War was a bad idea that should have been dropped on the cutting room floor or at the end of the pilot at worst. Series 2 didn't really go anywhere and every other episode seems to be "Archer gets captured by some aliens who beat the crap out of him, then the Enterprise comes in and rescues him in a big firefight".
One episode that struck me was the Cogenitor episode. I was completely expecting the aliens to go OMFG YOU BASTARDS YOU! DIE! DIE! DIE! ZAP-ZAP-KABLOINGK!. Instead, they expressed their sadness and... left. Now, in an TNG episode, that's what I'd have expected to happen and I was a bit startled: at what point did Star Trek go from the one being the norm to the other being the norm? Or am I just nostalgic?
Series 3, well, the less said the better. Might have been ok SF, but it was horrible Star Trek. BSG does the same thing much better. Series 4 was a step in the right direction but it was too little too late, too many people had decided the series sucked and stopped watching.
Sadly enough the Insurgency and Nemesis sucked the balls of a dead dog.
Actually, there was a lot about Insurrection that I liked more than First Contact, maybe because all I really wanted was more TNG episodes. Sadly, it did nothing to rectify my main gripe about First Contact, which was the new Enterprise. I couldn't care less about Kirk dieing at the end of Generations, but the destruction of the Enterprise made me really sad (more so because there was no plot reason to do it, unlike in Search for Spock).
Nemesis would have been a hell of a lot better if they'd kept in some of the deleted scenes and stuck with some of the original plans where they showed Shinzon earlier in the movie. Everyone already knew from reviews that he was supposed to be a Picard clone anyway.