Jason, your chart(s) almost exactly mirror Google Trends chart of activity. It's interesting. I've noticed it too...for a while now.
I too belong to many "online communities". The professional ones, the ones dedicated to business trades, mostly seem to be thriving as ever, at least the ones that were established in their respective space first, and that are well maintained and moderated against strict rules.
http://hvac-talk.com, or https://community.spiceworks.com/ for example, are two glaring exceptions to the general decline of online communities. 2coolFishing, TexasKayakFisherman are a couple of others that seem to be hanging in there too. Hunting and Fishing. Go figure.
Hobbies and interest type forums seem to be all suffering similar erosion of activity. Speaking for myself, social sites like FB have nothing to do with my ebbing/waning activity level in each of my memberships. Is there some overlap? Yes.
When I look at the charts you posted and consider the timeline, I can't help but think what a perfect storm of high speed mobile, matched with an explosive and non-stop supply "stuff" that interests, entertains, inflames, or otherwise seems to satisfy or satiate enough to gobble up available time during that period. I watch youngsters right now (High School), and indeed, people in any public setting and note how addicted they've become to their smartphones and reddit or whatever. I find it both amazing and scary. More and Faster...but not sure about Better.
What's next for HGCS? Well, I certainly don't know. I will say that the site continues to be an authoritative body of general geocaching knowledge on the Internet. At last look, Google has more than 160,000 references to HGCS.org posts, articles, and information. That's pretty cool if you ask me. It's worth preserving and sustaining. To do so probably will require some changes. This is definitely something worth talking about IMO.
I wonder how the analytics look Jason?
Our Garmin GPSMAP 62's are deteriorating after many years of caching abuse, so we're thinking of upgrading.
Since the 64's have been out for a couple of years now, are they still a good follow up to the 62?
Can y'all faithful users give a chime in about the durability, battery life, capacity, ease of use, reading the screen in sunlight...
You know all of those issues that are pesky...
I always stop by to take a look at what people are posting, but I don't start too many new topics.
It would be sad if this disappeared since this is one of the main ways that I can keep in touch with people about the Challenge and other events--we just don't make it down to Houston very often.