Vanheim isn't exactly a blood nation. The Vans remember how to sate nature with blood, but it isn't one of Vanheim's primary abilities. In other words, Vans are awfully expensive if you're going to use them as blood 1 mages
On the other hand, the occasional sacrifice to help spread dominion can be justified under some circumstances, and blood is the easiest path to "ramp up". In midgame, you can begin making an investment in blood, forge a few dousing rods, forge a few boosters, and you're on your way. Blood is hard to use on the battlefield, but Storm Demons are useful, and seem rather thematic as well. Enough blood can also alow you to diversify your magic. For instance, a Fallen Angel is a good fire mage, as well as a good blood mage, and can make a nice thug in a pinch.