I want to know why you feel the two skills are mutually exclusive. I'm pretty sure there are no µC/µP police who will break down your door for learning both. Moreover, I don't believe it will be appreciably (if at all) harder to learn both concurrently than it would be to learn either of them exclusively. But, and this is a big conjuction here, once you've learned both you will be in the enviable position to choose from a much larger selection which chip will best suit each of your future applications. That's my two cents worth.