Or make them free.
DLC is an awful model for the consumer. We already bought the game for 60-100$, what did we buy exsactly.
however, DLC was THE BEST IDEA THE GAMING MARKET COULD HAVE DONE, as a business looking for profit.
Put your self in [insert game company here] shoes. If you charge FULL price for a game then, have small micro transactions that cost the amount of candy bars or a cup of coffee, justifiy that reasoning to your consumer; Now 1 game can earn you a steady flow of money.
Subscribtions or a "season pass" idea works on big games like borderlands 2 or WoW because there is almost an infinate amount of content (or can be). When a game like COH2 (or an RTS) tries to, it is limited by "balance" and "Fairness".
DLC is not going anywhere if people (and they will in the age of spoiled children buying ANGRY BIRD, CANDY CRUSH, and FARMVILLE [i still dunno how people spend money on farmville]) continue to purchase micro transactions.
IMO/TL;DR: all these DLC should be free, as a consumer, we bought the game already, give me my money's worth. As a business, DLC is amazingly good profit.