Secondhand/new-old-stock Campag components tend to have higher resale value. This is the case even for 30+ years old components, and not just for the top-of-the-range group. In fact I think many have been appreciating in value in recent years.
Perhaps it is like comparing Porsche and VW, they are both great marques making great cars, but one has more of a connoisseur following because the other's product range extends to mass market offerings. Campag essentially only make and sell bike components, but about 25% of Shimano's business is in fishing equipment. Shimano has approximately 10,000 employees vs Campag's 700.