Spine fellowships can be obtained after either a Neurosurg or Ortho residency. Both N.S. and Orthopods are very good at taking care of the spine, no one is better than the other in general terms, it is surgeon dependant. I have scrubed with both N.S and Ortho Spine and I can say they were both very good. Spine fellowships are not very hard to get, only about 50% of the spine fellowships are filled each year. However, the top academic spine fellowships are tough to get, Case Western with Bohlman, UCSD, Wash U, etc. There is a difference between NS spine and Ortho Spine, Neurosurgeons can go past the dural sack to remove spinal tumors, whereas orthopods do NOT do that or want to go anywhere inside the sack. That is the only difference. About compensation, you can make a lot of money, some of the above figures are correct, academics is lower, 300-400s or so, private practice $600,000 and the sky is the limit.
The patient popultation is good if you are in a large academic setting which means you will get big/interesting cases (multi level fusion, front + back, Trauma cases, etc), however if you are in a community, you will do many diskectomies, and not much variety. That is why some people make the scarifse to work in academia.
The clinic can be a pain, and the patients are the hardest of all ortho patients to take care of post op. Most of them will complain of something, pain, hardware irriatation, etc. The surgeries work well, but success/pt satisfaction rate is not as good as elective sport/joint cases.
Most people in ortho do not go into ortho thinking that they will do spine, our program matched 2 guys to spine surgery fellowship last year, and they both wanted to do sports in the beginning.
About time per case, depends on the case, diskectomy is about 2 hrs, multilevel fusion w/ant and pos approach 6-8 hours, and I saw part of a case at UVA that was a sacraldectomy, complete sacrum removal for tumor with metal prostesis, that was about 25+ hours long. So the time varies. Taking care of the 16 year old in a MVA who loses sensation below the waist is not something everyone wants to do. Spine surgery has limits, pts like that probably will not get much better no matter what you do. You will not bring back function to the Extremities with spine surgery in the trauma setting, unless in very rare cases. However, you can prevent injuries with spinal surgery in pts with unstable fractures which can be satisfying.
Hope this clarify things for you guys.