Well, first off, Critical Care is a one-year fellowship following four years of anesthesiology, and Pain is a one-year fellowship following four years of anesthesiology. If you want to get certified in both, you'd have to do two separate fellowships, unless there are combined programs I don't know about (anyone?). If you were suggesting an either/or scenario, then I think you could do pain fellowship and then set-up in an outside clinic and not be a "hospitalist" if you wanted to go that route. There is a big demand for pain specialists right now with commensurate compensation. Whether that continues will depend on how many enter the field over the next 5-10 years.
The pain guy I worked with actually had a sweet deal. The hospital he was working at was very interested in setting-up a pain service. So, they basically gave him an off-site clinic where he could see patients provided that he did all of his procedures in their ambulatory center. So, essentially, he gets to see patients in his office (that they pay for) but does all the procedures in their facility. This is win-win for both because he gets a free office and the hospital gets him to bring patients into their ambulatory center, which they get to bill for. The only downside, as I could see it, is that they required him to manage the in-hospital pain service (i.e., he had to round on all of the patients on PCA). Although, he usually just got a resident to do this part for him, collect the notes, review and sign-off, and then have a resident or student re-insert the notes in the chart. So, it wasn't that "painful" for him (pun intended

). Also, part of the deal was he covered the OR on Fridays if they needed an extra anesthesiologist.
-Skip