I suppose the first thing to do would be to identify the areas in which your clan is lacking. For us, it was in-game, so we started pushing war activity really hard. I'm not sure, but I think you guys have got ingame activity sorted, so it might be time to start focusing more on the forum side? You guys use Skype, so IRC activity isn't an issue.

I'm not sure that restricting growth by maintaining a member cap (it's 15, right?) is a good idea. I can see the reasons why you have it (stability), but I think it'd be better to focus on stability after acquiring a larger base (and the activity benefits that come from having a larger base).

Lastly, I'm not sure if it really does affect activity (it could, but it also might not), but requiring tags at the end of posts is a barrier to posting. You could probably squeeze out more forum activity by removing them. Then again, it's (le)'s schtick and it differentiates it from other clans - so, I'm not really sure if the potential cons outweighs the pros.

tl;dr;
Step 1: Identify problems/inadequacies/inefficiencies.
Step 2: Crowdsource solutions for them.

[General]