My 2013 Vstrom also has a recommended interval of 12000km, which I think is a wasteful interval.
I'm nearly at 36000km so I should be changing them for a 2nd time already according to the manual, but I haven't; not because of the cost -- the new plugs are sitting in my toolbox -- but more because I need to take off the fairings, gas tank, and move the radiator to get to the plugs. One of these days I will work up the energy to do that.
Suzuki also has ridiculous intervals for a coolant change (12000 if green coolant), while I think they suggest too long an interval for an oil filter change (18000km). I haven't changed my coolant yet, but I test it to make sure it is still effective. I change my oil filter at every oil change -- I think this little engine deserves it.