Much will depend on where you will be going and at what time. I would really not recommend wearing very much jewelry while off the ship if any at all, and even then, not the 'good' stuff. You should always use common sense and realize that in many areas, you are setting yourself up as a 'rich American'. Now of course if you are visiting Monte Carlo I don't think you will attract much attention but obviously there is a differant degree of wealth there. Leave it on the ship and break it out for the formal evenings, other than that, leave it in the safe.
Just replied to your question about jewelry aboard. Please see my posting entitled Jewelry on Cruises above. I intended that it would answer your query but did something wrong and it went on the board as a new posting.