I'm not buying these to change tubes, I'm happy with the tubes that are in there. I'm just buying a backup set of power tubes in case mine go out before tubes are available again. I agree with you though, I don't know much about speakers but pickups/pedals will make more of a difference in your sound most likely.
The tubes that are in your amp will most likely last years and years as long as you don't abuse your amp. True, backup tubes never can hurt but they are available and will be. They aren't going away.