I bought a 3DS XL to get this game, yes it is worth it.
You can solo through the full game, low rank, hi rank and G rank. You can also connect online and download all the event quests, and play them anytime. So unlike Tri the full game is always available.
For 3DS Multiplayer you can connect with other 3DS players to play locally, you can also do that with a WiiU. Additionally if you have both the 3DS and WiiU versions of the game you can transfer your character between the two so that's cool.