First, let me state that I appreciate your commitment to the hobby. As life goes on, lots of stuff gets added to our daily load (much without our permission) so it takes a lot to keep this going in the overall perspective of your life. I haven't posted here in a long time due to some of those same kinds of additional responsibilities. I'm trying to get back as life allows, and I think I'm making some progress.
My vote is to keep the technical content and discussions as long as possible. Facebook and other such social media are great for a lot of "current" events, but it sucks when it comes to looking back at what blue81ta did when he had that problem with his water pump.
The eBay stuff prior to a certain date (fairly recent date) could be flushed. The other "for sale" or "wanted" content could probably be flushed if it were older than 6 months. Basically, anything that's no longer relevant could be dumped to save space.
The small talk social stuff should expire after a relatively short period anyway. That's the strong suit for other social media, but I think it has a place here for those who are so inclined -- but not to the point that it drives you to distraction or causes you unneeded expense.
So I approve of the proposed moves with the above qualifications, but I'm only 1 vote and the guy who holds the key vote is the guy who has to actually execute the plan (Brett)!
Finally, don't be embarrassed to pass the hat if it's needed!