Don’t pay through the nose for one. They’re old systems and should not be considered reliable (though, they may be).

The value in a 3DS is the jailbreak. Once you have the “H-shop” replacement for Nintendo’s E-shop, you can basically download any game that was available digitally. You can also dump your cartridge-based games, save some wear and tear on the slot. I know some people value physical, and that’s a fine point, but it’s also true that the card slot is an (eventual) failure point, and it’s one you can eliminate.

Another cool thing you can do with a 3DS is dump the saves and restore them. I have Animal Crossing: New Leaf on cart, but I’ve dumped it to digital. I also play (mostly play) on my MacBook Air via an emulator. If I think I might be going back to the 3DS, I can put the save game back on the 3DS and pick up right where I left off from on the computer. There’s also a level editor online, you browse to your save, you can make your whole town green again (no dead grass), you can touch up locations or straight up move stuff around, you can even reroute rivers and such. Just note there are a few checks the game makes (when Isabelle says “getting the town ready”) and if it fails any checks, your save won’t load. So don’t go too crazy. If the game won’t let you do it, like place a lamp post in front of a neighbour’s door, that might make it fail the check. By the same token, the game itself is overly conservative with placement, but the check, not so much. You can definitely move a light post one space closer to a bridge than the game will let you place it. I’ve done this — I don’t need to be able to walk between the light post and the edge of a bridge. The game makes you place it a full space apart, but the check doesn’t care if it’s now right next to it. But always keep the old save, and only make one controversial change, and verify the change passes the check.