From a commercial standpoint yes, from a show ring standpoint not so much, unless you've got a nice wether to compete with.
We have a couple of couple of Spanish does- they're our best mothers and the easiest keepers in the group. They're also the wildest goats in the pasture though. We breed to fullblood boer bucks, and the kids turn out pretty nicely. The boer adds some mass and docility, while the Spanish adds hardiness that you just don't see as much in the fullblood kids.
I feel in our area you would be limiting your market by adding Spanish to the mix. If your goal is purely hardiness and meat, then you would be okay. but if you are looking to sell replacement breeding stock and hit a little bigger market you would be better off sticking with Boer goats with no Spanish in them, or Boer/dairy crosses with really good frame and thickness. True they are not as hardy as the Spanish mixes. But with the wether market in many areas bringing top dollar and wether maker does bringing very good money, in my opinion you would be some what limiting your market by going with just Boer/Spanish does. No reason you couldn't try a mix of different does and breed to a nice Boer buck and see what you think and who sells the best.