Two things.
The more rules a forum/mailing list has the less likely I am interested in posting/going to it. There's a lot of FS/FT/WTB posts here but there's nothing preventing anyone from posting the kinds of things that you're looking for. A lot of people choose to post patch and performance examples elsewhere like Muff Wiggler and Quadslope. This forum would probably also get a lot more traffic if someone from STS posted here like Cynthia does on the Cyndustries mailing list but I'm sure Rex isn't interested in something like that.
Secondly, wouldn't we want people bringing their Serges here or other modular forums/lists for sale, first? They're much more likely to find an appreciative, reliable and honest buyer here than on Ebay or anywhere else. The last place I'd suggest a friend sell their items is Ebay but it's often the first place they think of.
We'd all like less Craigslist-like ads here but a big part of being a modular enthusiast is buying, selling and trading things. It just is. People are always looking to expand and change their systems and some come to the realization that Serge/STS is not for them.