Must be nice to have all that money. Hahaha. I do wanna get a second copy for ACNL. Not six, but a second. So I can work on my weeding badge and cycle out villagers. If I have the money and find a used cheaper copy, I will buy it eventually.
Most people buy tons of cartridges. (Honestly idk why someone would buy 3 3DSes just to have multiple towns lol)
But if someone's a hacky like me, they can just backup their town, reset, keep the old town backup and backup the new town. Boom, 2 towns on one game. Then they just import the backup of whatever town they want to play on.
Well I have multiple cartridges AND multiple 3DSes (I kinda collect them...lol), but having more than one town on a single cartridge is entirely possible. If you have a PowerSave, you can create backup save files and swap out the towns that way.
I have two cartridges but only one town. Had two towns once but it became to much for me to manage. I don't know how people have the energy for six towns.