I think New 3DS XL will worth it because it has many advantages over old 3DS or its XL variants, like having C-Stick to add more controls in Smash, and having ZL and LR buttons as the bonus. Besides, it could start up the games faster, including Smash, and you can quit playing Smash/newer Monster Hunter games with the Home button faster without need to reboot like in old 3DSes.
You can also play with automatic brightness setting, which means you can play your games in dark areas without worrying about the screen being too bright, and you can also utilize your Amiibos straight away to your handheld, so if you want to upgrade to New 3DS (regular or XL), it'll be worth it.