I agree that unfortunately in anesthesia, your income does not increase with specialization.
Cardiac: Make more per case, but tend to work longer hours so income per hour is about the same.
Peds: May actually make less because you're mostly doing ASA 1 cases, plus you're likely to be practicing in an urban area with a larger population of indigent non-insured patients
OB: Make about the same as a general anesthesiologist, less if you're doing high risk and have higher malpractice
Critical Care: Almost always make less than a general anesthesiologist, hence fellowship programs are desperate for applicants