Whether one chooses to spend the money or not is purely a personal choice. In a blind test using two models of guns, a friend and I were able to discern which guns had the lengthened cones about 94% of the time; well beyond coincidence. I also got approximately 3 to 4% better patterns. Got the same from overboring, but the results were not addiditve; 4 to 5% max. All of these results were with heavy loads of #4 shot and larger, and plastic shotgups.
I have not overbored any SxSs, but I did have the forcing cones lengthened on two with no ill effects.