We discuss the impact of Sommerfeld enhancements on the neutralino LSP relic abundance calculation for heavy neutralino dark matter including co-annihilations of nearly mass-degenerate neutralino and chargino states. Interesting regions in the MSSM parameter space are identified, focusing on heavy wino- and higgsino-like dark matter scenarios and models interpolating between the two cases. We investigate several benchmark scenarios in this part of the parameter space. Sommerfeld enhancements in all (co-)annihilation processes of (nearly) mass-degenerate neutralino and chargino states are considered, including P- and next-to-next-to-leading order S-wave annihilations. A newly developed method enables us in addition to treat effects from heavy states perturbatively in the Sommerfeld enhanced rates. Our generic analytic calculation of all (off)-diagonal potential and annihilation matrices allows for the first time a rigorous study of Sommerfeld enhancements in neutralino and chargino pair-annihilations in the general MSSM.