When I was racing back in the 80's and 90's I would stretch my sewups, Conti 250 sprinters and Vittoria Corsa GTs, on old rims, inflate them and store them in a closet. Usually for the season as spares or the next season as needed. Whether it made them "better"...eh who knows. I certainly could not tell the difference but riding/racing on sewups is awesome.
Miss them but not the cost and effort lol.