hmmm...i'll answer this since i'm in a similar situation.
Risks:
takes a lot of time to study / juggle work, family, school
costs a lot of money
the MBA may or may not help you in the long run depending on your career goals and objectives
possible opportunity cost loss by focusing on school and reducing your focus on work
Rewards:
33 isn't that old and 36 isn't that old. Assuming that you work until 60, you'll have the benefit of your MBA for 24 years.
Depending on how much more you think you can get paid, the MBA will pay for itself + more.
lots of learning and gaining of new knowledge
many more connections established
potential for higher pay
potential for industry change
I think in general, the rewards far outweigh the risks. but then again, you're talking to a guy who decided that getting an MBA (i'm 35 now) is worth it so i just started at the Wharton MBA for Executives programs.
RVD.