I switched to Xenforo in the beginning of 2015. That may have slowed the decline a touch, but the trend has still been downward.
No competitor has arisen to cause me to rank lower. We're still by far the most active site in our niche, and there is no new site in our niche. Facebook hasn't supplanted us in the rankings. It's the same bunch of sites as ever, just us ranking lower than the non-forum based sites we used to outrank. Our forums are as active as ever with great content contributed daily.
More recently I made quite a few changes to try and turn this around:
-Less above the fold ads
-Change to https
-Add http/2 support
-Various speed tweaks
-Increased frequency of sitemap submission to daily
-Removed Recent Discussions from sidebar for guests
The very last change I made was to convert from full friendly URLs without content title in URLs (nice and short URLs) to full friendly URLs with content title in URLs (longer but keyword rich).
It could be a coincidence, but this latest change was quickly followed by an uptick in search traffic:
I am hoping that this trend will continue. If it doesn't, I may go ahead and drop ads entirely in hopes of doing better with the next Google Panda update.
Would appreciate feedback as to whether you think my site has too many ads and/or there are other things I can do to improve search presence.
One good thing on the horizon for those of us using https and http/2 is that the GoogleBot will soon support http/2.