Replacing entire group - need new hubs?
With that in mind - can I put a 10/11 speed cassette on my existing
  (15 yr old Chris King) rear hub?


9, 10 and 11 speed Shimano MTB cassettes all use the same freehub body, you can keep the old hubs.


  It has come time to replace the rings (3rd set) again but Im guessing
  that I need new cranks.


Given a 15 years mark, you run FC-M950 or FC-M952. If that's true, try looking for an aftermarket directmount spider that accepts more readily available chainrings. Personally, I find it quite cool to own one of a kind crank like that.