Reimbursement is based largely on procedures nowadays. In other words, more weight is based on physicians who DO, rather than RUMINATE. This is essentially why Internists are near the bottom of the ladder (fighting it out with FPs for bottom-dwelling status). While there are procedure-heavy subspecialties, including Cardiology and GI, Rheum and Endo are the other side of the spectrum. They do not do procedures; Rheum spends all its time looking at your auto-antibody titers and Endo touches itself while they look at your glucose logs. On the other hand, they are also relatively cushy specialities, with no call/emergencies (well, ones that specifically require them rather than a general Internist).
Nope. Reimbursement levels don't go up just because you're a subspecialist. They are set by the third-party payers and they are pretty uniform -- you do a procedure you get money, you don't and you get some acorns.