welcome to (mac)retrobike Steve,
I'm also in lanarkshire, a handfull of miles from you in larkhall originally hamilton (always got to throw that bit in so i'm not assumed to be a the rangers fan)
definitely keep the kona, you'd only regret it
riding out from the house, i generally use chatelherault, strathclyde park, barons haugh natural reserve, clyde walk way, new lanark trails as they're all connected. not exactly wonder single track stuff, but it keeps you off the road and has many options allowing a 30min to 3hr run with minimal tarmac.
if these interest I'm you happy to share the detail, or show about them. although it's all skinny wheel road miles for me until mid oct
sounds like you've been riding over the ardochrig road at whitelees, a particular road bike fav of mine, do a fair few road miles taking in glassford, sanford, muirkirk, waterside, clyde valley etc
tbh i don't know of any great single track to us locally, certainly nothing thats going to compare to the runs you mentioned earlier. would be interested in hearing about the ayrshire single track if you find it.