Oh, want another 'Scare em away' factor? Look at the other end of the market, when they want to get rid of their gem. Read the threads directed towards me and a $95,000 price tag on my plane. Why would anyone want to add themselves into the middle of a group of hyenas?
I personally thought your price tag was "close" to right. The thing keeping your aircraft from selling is the 23-26 GPH to operate it.
You mention that you fly it LOP and baby it... and many would, but there's a portion of the crowd that would want a 310 who would want to fly it around balls-to-the-wall, and the fuel costs are too high compared to a slicker, faster, modern single.
Many of us understand the utility and possibly even the safety (if flown correctly and the pilot stays current and gets appropriate regular training) of the twin, but the care and feeding of two 13 GPH engines, plus reserve, is beyond reach for many fully-aviation-addicted folk, without a lot of partners.
I love the C-310 ... in my head. I look at the operating cost numbers and think... "insanity". It's a light twin from an era of $1/gal fuel.
The things you've done to it, make it a great personal transportation tool, but the kids who are building time are going to buy a clap-trap 310 that has solid engines and trashed interior and fly the snot out of it and sell it at a loss, just to put twin time in their logs. Personal flyers are going to balk at the operating costs.
So, that leaves your 310 a bit "lost" in the middle. Too nice to beat up to build time in, and too just a touch too expensive to operate as a personal transportation machine unless you're the type that MUST have two engines.
The ENTIRE market is also in a very bad place for "step-up" upgrades, since most folks who'd want your 310 already own something else they probably couldn't sell easily... and that they just might be upside-down in. The problem "trickles up" so to speak. I'm not sure what breaks that cycle other than a whole bunch of folks collectively taking a fiscal drowning.