Can you afford it? It honestly depends on how much you honestly feel you will be playing the system. If you're like me, and you bought it for smash and haven't really used it that much, then you're better off just keeping the one you have. If you plan on playing the 3DS version of smash as your main game, then invest into it.
Honestly, given the fact that the new 3DS was announced, I would just wait it out and do the best with what you have. At one point I contemplated just selling my 3DS after the Wii I version came out, but playing smash on the go is something I've been wanting since I was a kid so I'll probably hold on to it. I think the regular 3DS is fine, and I'm 6"1 with pretty big hands. I honestly like it more because of it's portability.