My initial thought is that Clarke will be taking up a pretty large portion of the salary cap to play as 3rd, or maybe joint 2nd, choice hooker. Based on that I would rather, if we can find a club and terms agreeable to all, offload Clarke.
However, I prefer to go into a game with a bench consisting of 2 props, a hooker and a utility player (preferabley a forward). On reflection, and having read some comments on this thread, Jon Clarke is an ideal utility interchange. As has been said he can cover halfback, second row, loose and (obviously) hooker.
Given a choice between VAnderson or Clarke as 17th man I would take Clarke every time. The more likely choice between Clarke or Grix as 17th man is far more difficult and I suspect would depend very much on the opposition, weather/ground conditions and probably most importantly, minor (ie players can still play but...) injuries to any of the other 16.