Try to learn Android and you raise your market value multifold. I would however though learn a scripting language to have a complementary skill-set and put a framework on top of that. I'd recommend Ruby --> Ruby on Rails.
Android is built on Java so learning Android programming is as simple as learning the ins and outs of an Android program rather than a whole new language.
Android won't necessarily increase your market value more than Ruby but it will be a much easier thing to learn considering you already know Java.