I have a cruise booked and I check the price daily. The funny thing is, often from the end of a sale to the new one...there is no change...or it goes up or down slightly. Keep in mind too that if you have booked and the price drops before your final payment, then you can call in and get the lower price. Also note that if you call in for a price drop, that you must take into any account on any OBC, etc, as the original booking will be lost (but new offer will get applied).
Royal has recently introduced 'refundable' and 'non-refundable' prices. If you book by non-refundable, then you can cancel any time up to final payment date. If you book refundable, then you will lose $100 per person of your deposit.