Out of the two remaining shows, DSN would be the cheaper of the two to remaster. As it has far fewer CGI elements than VOY.
So whilst it might not sell as many units as VOY, the lower cost might counter-act that.
You've also got to consider that it might make it more attractive for networks to repeat.
Despite being one of the more critically acclaimed shows, and it topping polls (or near top) of favourite Trek shows. It is one of the ones to air less frequently.