One thing I do want to mention is, I think the real reason for the decline is probably the simple fact that there really isn't a good way to keep new members coming in, while old members will drop off from time to time. I think the retention here is actually pretty amazing compared to other forums I've posted on (for example, the poker forums seem to be filled with a whole new crop of people every year with only a few familiar voices, and the size of that forum is enormous).

I always wished this board could've made a transition into a community that would be able to find and retain like minded individuals rather than being based on the empeg player, but I wouldn't even know how to define our common link except to say "cool, mostly semi-geeky people that are worth listening to".

Ever thought of sending a hey we're still here email out to everybody registered?

Those could have been my words. I agree so much with you.
Personally, I just find that I just found myself with much less spare time, over the years, and that is the first reason why I tend to post less. The second being, by far less relevant, that there's so much less to read about the Empeg itself.
Still, surprisingly, I keep coming back, and I actually never felt I left this place. I've met only few of the board emmbers in person, and still I feel so much part of it.

Did people leave the board because of religious or political topics? Some may. It is unavoidable. "religion wars", be them about actual religion, or politics, or Microsoft vs Apple vs *nix, are such that invovled parties do not feel welcomed or respected by their counterparts (opponents?).
Still, I feel most times such heated discussions, here, were not nearly as bad as in most other forums I've been on. In several cases, they were instead enriching and respectful. Some of those discussions are actually one of the reason why I am still here.

Don't forget, just because some of us don't have the time to devote to reading the boards as often as we used to, doesn't mean we're gone. Personally, I just don't have the time. When I joined, oh a decade or so ago, I'd read effectively every post on here, daily. Now I check in when I can (and remember to), but sometimes there could be months in between. Even so, I shudder at the thought of this little corner of the web ceasing to exist. For vast amounts of my adult life, the forums have been my internet "home". A place where we can talk pretty openly without being verbally abused by random trolls constantly.