I don't mind too much if a blockade doesn't contribute to the Warscore (though a small contribution would be welcome) as long as a blockaded planet does not contribute resources or research to that empire. If the resources are stockpiled on the planet and released to the owning empire when the blockade is lifted then there would be an incentive to relieve small blockading squadrons with smaller fleets rather than your Doomstack; which would be interesting.