I doubt anyone here has had rougher hands than me(never need a glove), so I don't change grips very often.(after not working for 5 mo. now, they are losing their roughness--my hands) OTOH, I take care of my grips, always. A new set will last me a few years, and still be tacky if someone else were to try the clubs.
And yes, new grips consideration should add, or detract, value from used clubs, buying or selling. I'm not about to buy a set of irons that need grips straight away, unless they are priced accordingly or seller will drop pricing to compensate for such.