Just thought I'd mention that you don't have to spread rules if you don't want to. There are different rules inherent to each region, but you don't have to spread them to regions that don't have the same rules.

Say when you come back from Esthar and you try to play someone in Balamb. When you challenge them to a game, there's the obligatory "Oh, I see you've been here and here; let's play with those rules etc.". Just say no, and the rule(s) won't be adopted into the region. Challenge the person again, and they may again mention something about foreign rules, but keep saying no and challenging him/her until he/she goes straight to asking for a card game. Then accept their proposal.