Actually, 3db is smallest amount of difference that you can hear, so the car will be quieter than before. More importantly the doors will feel more solid.50mph - Before 73db -- After 70db (3db improvement)
60mph - Before 77db -- After 72db (5db improvement)
70mph - Before 80db -- After 73db (7db improvement)
I would have to agree, for 3, 5, 7db improvement wouldn't be my goal for a project like this.. 10, 15, 17 maybe...
Everybody needs to decide if an improvement is "worth it". If he was expecting a 20db decrease then it isn't worth it, but if he was interested in an incremental decrease, then he got it.
That said, 73db at 50mph seems a bit loud as a baseline.