I bought the permanent docking kit a while ago, and installed it using a home-made custom mount on the dash (it hooks securely behind the trim and doesn't require drilling.) The TomTom shoe is permanently bolted to that, and I've left it in place in some pretty dodgy areas. I keep meaning to rig up something that will let me disguise it as a can of pop in its holder
Touch wood, I've yet to have a problem (but never say never.) I don't think the crooks actually recognise a dash mounted TT shoe - they're too busy looking out for the suction cup attached to the windscreen.
I've PIN coded my GO now as well. I don't know how effective this is, but at least as mine's a 700, there should be more to disabling it than buying a new SD card.
As for the docking kit - I'm about to rip the damned thing out and replace it with the standard antenna shoe. Most of the supposed advantages of the docking kit don't actually work properly (e.g. voice through the radio speakers) and those that do (e.g. link night view to headlights) turn out to be less useful than you imagined when you bought the unit. In fairness, this kit worked well in my L2 Phase 1 apart from the CANbus noise through the speakers, but it's been an absolute nightmare in the Phase 2. I've even hacked the PDK loom to take power straight from the central locking switch - that's cured the 'switching off randomly and frequently' fault, but it still manages to light the front panel LED but run the battery flat. The TT works fine and charges normally when hooked onto a normal shoe and charged with the cigar lighter adapter. I can only conclude that the TomTom PDK is a badly concieved and badly implemented piece of tat
Anyway, I'm rambling again