I would not pursue a specialty in the hopes of making a higher income. Specialize because you want to and are passionate about that field. I've applied to surgery residencies this year (for the first time) and am prepared to complete multiple surgery internships if I have to in order to become a surgeon. I know many surgery residents who completed 2-4 surgery internships before matching to a residency, and they were making $25-30k annually during this time. That's an extra 6-10 years where they could've been making $30-40k more as a GP out in practice.