The first region locked nintendo thingy was the NES.
I'd buy a new advance wars. And a 3DS with it. I'll buy a 3DS eventually anyway, it just needs a good game as an excuse for me to buy it.
Advance Wars DS did that with the DS.
I enjoyed Advance Wars Dark Conflict, but it didn't have a lot of replayability. The story was good though.
I even bought the american localisation Days of Ruin because it had different dialogue and alternate names (and was cheap.)
But Dark Conflict/Days of Ruin/Lost light as it would have been called in japanese isn't out yet in Japan (cancelled) and I don't know the reason for that. Probably the same reason why they won't make a next game.