I love my CTDS. It makes me play Chrono a lot more often, and just think, man. Portable Chrono Trigger! Going to 7-11? It's CT time!
Going on a plane? It's CT time!
Going to a third world country? Guess what time it is!
Seriously though, it's pretty cool. I haven't touched the arena cause the concept reminds me of pokemon, and I don't want the two franchises to mix in my mind. However, the extra stuff is very cool, theres a Bestiary, movie player for all your cutscenes, music player for every song in the game, a couple different options to battle. Almost all the battle stuff is on the extra screen so you get a better view and they run more seamlessly than in the snes version. There is no lag whatsoever. That alone makes it exponentially better than the PSX version, which had a lag every time you went to the menu, or a battle, so much that it rendered it unplayable for many. The new script keeps references to things that were censored or localized, but retains the original spirit of the game, and retains the humor. If you've played the game before, the script will be very familiar, but it's still a new way of experiencing the game.
Not to mention my favorite part. The menus. Not the battle menu, I still just mash A a lot while grinding, but the store menu and the regular push X menu are on the touch screen, which makes navigating through them and getting what you need done much easier and faster so you can get back into the game quickly.
The new maps are okay... C99 did a better job on some of the CE maps, frankly. But it is a new area with new implications and new plot to be considered. I think it's worth it. I actually posed the same question, except I didn't have a DS. I bought the DS FOR the game and I do not regret it one bit!