Put simply I don't think coh is modern enough to attract much new blood. I get the piss taken out of me at work by younger gamers for playing coh. It's in a light hearted way but it shows that its only appealing to the old guard because, well, its old. I've been waiting for a relevant thread to bring that up. Not sure much could be done because to get more people interested I'm sure the answer would be to change the game itself.
Take a look at Final Fantasy. They had to stop selling it because its so popular. It's the new, up to date kid on the block.