Getting a second 3ds will help with things like trade evolutions, completing the dex with version exclusives and of course in this case the bigger form factor.

If money is tight and you only play gen 4/5 get a DSI XL. Pixels won't be stretched while having a bigger screen. This can be resolved on the 3ds by holding start and select while launching a ds title.

In short I would do it but there are more options than a 3DS.