Don't bother with Pro Nav. Use TomTom for the few times you need it.
It will affect the resale value, but not by anywhere near £2k.
Unfortunately everyone who has it will tell you to get it (since they rationalised it to themselves) and everyone who doesn't will tell you not to (for the same reasons).
Only solutions is do what's right for you for your reasons.
Last edited by steddyman; 12-12-2013 at 08:12 PM.