Adjusting speeds outside the POH is just poor pilot skills and you will get caught with your pants down eventually.
Nowhere in my POH does it say anything about adjusting the speeds for gusty conditions. It does state that all figures in the POH are subject to the aircraft being flown exactly at the stated numbers.
Learning to fly at the correct numbers is all about becoming a good and safe pilot, adding rules of thumb and old wives tales is about being an average pilot. Most of the time the average pilot gets away with it, the times that they don't makes for entertaining reading in the AIB reports or to often sobering reading...........