A pound a corner of unsprung weight is definitely important. Will it mean the difference between winning and losing? Probably not, but combined with a dozen or more other "little" things, it adds up to an appreciable difference that can give you a tenth or two here and there. When racing, the rules have to be maximized in order to develop a competitive car. It's part of the game.
After all, F1 teams have $400M annual budgets. They don't spend it all on post-race parties.
On the street, you would be hard-pressed to appreciate the difference.
Ara