I see it this way: AこそあれB = Although A is negative, there is something good B about it. (Although studying takes a lot of time, it'll help you become more proficient). AこそすれB = Even though A (something good [quality/action]), ultimately B (something that can't be done, or some negative event/action).
ok I've gained some new insight since I last looked at this ;-) while I now agree with your assessment of こそあれ, it seems that the tone of both parts of こぞすれ should be roughly the same (I'll re-post what I mean over there)
