Well, you have to play it on 'True Valt Hunter Mode' in order to unlock the extra levels. So if you're down with playing through it again at a higher difficulty, with new and tougher enemies, then yeah, it's totally worth it. Honestly, it's the DLC I'd recommend buying last as it doesn't really do you any good to play it until you've reached level 50.
If you're not into playing it again on hard mode, then you're probably better off without it. Mr. Torgue's DLC is also a blast. The Pirate one is okay, still worth playing but not near as good as Mr. Torgue or Tiny Tina's DLC. I didn't care much for the Hunt. It wasn't horrible or bad, just didn't do anything for me, wasn't particularly funny and it was over pretty quickly.
Though, you should get Assault on Dragon Keep. Don't play it until you've finished the main quest though, as there are major spoilers involved. Mr. Torgue is also totally worth the money. Those are the two DLC you shouldn't miss for this game. The UVH DLC is worth it if you're really into the game and don't mind playing it on a much harder setting. The other two are also fun, but not essential. Captain Scarlett's is better than Sir Hammerlock's DLC.
If you really like the game, get them all. Play through Tiny Tina last though. It has the most awesome weapons. Like grenades that regenerate and act like spell castings rather grenades, and a gun that shoots swords and uses shotgun ammo and also the most awesome weapon dispenser in the game [it's not one of the vending machines]. It's best to pick these up at lvl 50 or so as they're very useful for going through the game on True Vault Hunter Mode. I'd wait until lvl 60 to do it the second time through for the same reason. They're dead useful and you want to get them at the highest possible level.
TL;DR: Depends on how much you like the game and whether or not you're interested in playing through it again on a harder difficulty or not. If so, then yeah, it's worth it.