I have a K1300R for nearly 5yrs now, I think it's a great bike, I don't generally see the point in the the 'S' just adds a screen which is too small anyways and bunch of useless expensive plastics. I'd make sure you find a bike with the quickshifter because that sounds amazing with even the stock exhaust. Not had too many issues with mine though its pretty low mileage now except a failed left switch gear last year (common failure, mine where replaced when bike was new too) which all considered for 5yrs of running is pretty good, apparently the newer parts are more reliable and certainly feel different.
Above comment really goes to show people have different opinions, I think the bike has great character and the engine is really amazing. It's only real downsides in my view is it is a bit heavy, I don't find the seating position as comfy now that I've got an S1000XR and in town it's a bit snatchy compared to the new breed of fly by wire throttle bikes.