Managed to resolve the marker positioning problem by going off for a rather nice meal with friends and family - on returning to the coding environment, the solution that had eluded me most of the day was suddenly blindingly obvious... With that hurdle cleared, the remaining updates fell neatly into place, with the result that version 2.0 is ready for release somewhat sooner than expected
The majority of the changes in 2.0 are behind the scenes, however sharp-eyed users will notice a new option lurking at the bottom of the UI - "Hide Livemap markers". Since the new Livemap doesn't appear to have any way of natively hiding the traffic/event markers that clutter up the map even more than they did in the old Livemap, this option allows them all to be nuked from orbit, leaving the map nice and clean - at least until it starts getting filled up with LMUR-generated markers instead...
Firefox+Greasemonkey version: http://userscripts.org/scripts/show/150276
Chrome packaged version: http://crx.chizzum.com/LMUR.crx