This isn't really accurate. They added at least four new dungeons, several new bosses, new ways to get tabs, a way to up some stats that couldn't be boosted before, and a lot of other stuff. Some of the dungeons aren't so great, but otherwise work well for the game. Overall, it's the best version released so far. If you can find it, and you think you'd be interested, pick it up. If not, stick with the SNES version, because the PSX one has terrible loading times.
I combined 3 of the dungeons into one (and the two Prehistoric dungeons into one as well) when I talked about them because they are just extensions of the same two quests, and they're just remixed versions of existing environments anyway. None of the dungeons were all that fun to go through in my experience, though it was nice to hear one of the missing musical tracks from the original CT score finally used there. I don't remember the new way to get tabs, but whatever. The game's easy enough that you really don't need those tabs anyway. As for the "new bosses", I can only remember two new bosses: one of which is tied to one of the new dungeons, and another that's part of the new DS-exclusive ending. I don't remember finding either boss all that notable, especially the one that's part of Square-Enix's eternal struggle to force us to accept Chrono Cross as a legitimate sequel to Trigger.
With the original SNES version of CT already confirmed for the Virtual Console in two regions (and highly likely to reach our NA one at some point this year), I just can't recommend picking up the DS version when the things the DS version really didn't add much that improved the game and the VC version will be cheaper anyway. Now, if we
weren't extremely likely to get the game on the VC, sure I'd recommend the DS version in a heartbeat (especially over the craptacular PS1 version).