If you are talking about the 3D content alone, then no, it's probably not worth playing just for that. That is to say, if this were literally the N64 title in 3D, then it would be a gimmick. The combination of the 3D, the revamped graphics, refined controls (based on comments about ease of item handling from developers) and additional content -- this is what makes it worth playing. It's the same game, but revamped, tweaked and perfected even beyond what many believe to already be perfection.
On that matter, for the developers to decide to remake the game says right there that the game is not perfect. I think if the people who created the game felt it was indeed perfect they wouldn't touch it. I also don't believe any game is perfect, because they all suffer from minor blemishes. For OoT, graphics are a bit choppy (even for it's day), and controls are sloppy in places; the boot-switch-out in the Water Temple being specifically cited in interviews. Don't get me wrong, it's still a magnificent title, and at it's "worst" is infinitely better than most drivel released, but it cannot be said that it's truly perfect. If it were, Youtube wouldn't be chocked full of glitch exploiting videos.
The combination of the 3d, the graphics, the control tweak and whatever other bonus content surprises they have in store make it worth while. Plus, an entirely new generation of people who haven't experienced the game now can in a new way. Yes, the game's out there and available for download currently, but Nintendo themselves have admitted the Virtual Console is not reaching as many people as it should. People will play OoT3D who have never played it before, so it can't be said it's a total loss.
As someone who owns multiple versions of the title, it's still a deciding factory in the positive to buy an entirely new console. The game's just that good, and tweaked it will be even better.