Limit acquisition of off element cards from merchants:
One possible way to do this would for the NPC merchants in each town to only offer cards of that town's element, and for them to only be willing to sell to players either belonging to that element, allied with that element, or possessing a very high Rep with that element. This would make trading and Auctioning one of the primary ways to get cards of off elements.
More importantly, it gives UW a very viable income route through their Bargaining/Trading skills as "black market" dealers for cards not available to other players. Of course, this only works if the UW merchants are accessible to normal players or they will simply travel to Outlaw City and buy everything they need there sans trading.
I live the no-salvage idea alot SG. I'm not even sure you have to give
for winning battles. If you remove the main source of income generation from battles (cards) it will encourage players to interact more like a RPG and less like a "dungeon crawl" where you just kill and live off your loot.
100% agree with YoungSot on the restricted cards in towns idea. The only faction that should have all element cards available to them through a merchant is UW. If you want cards from other elements, you should have to travel to that elements lands, or barter with elementals. This will give players no incentive to hesitate before Capturing or Attacking other elementals since starting a War will close off the merchant card sources and force every player of that element to pay the premium "black market" prices.