Should I update my 3ds from 9.5-22U to 9.9

I have seen that the new animal crossing game needs the NFC Reader/writer, but, one of my 3ds is on a lower firmware.
I can use the spider hacks, but I want to use the new animal crossing.
I have 2 3DSs and ones an XL the other is a regular, should I update BOTH? one is already on 9.9, so. I'm sorta freaking out. I can't use the NFC Reader for my XL. What do I do?