Always disappoints me when I hear of people going every year with the same cruise company so they mount up their loyalty points. Greatest considerations should be ports of call and quality of service. This ranges from ship to ship and we have found that there is little difference between the "big boys" since a lot of them are owned by the same group. However we have been pleased when booking with one of the cruise companies we have been with before that we have been given free transfers to Southampton and on board credit. Despite these small surprises though it has not put us off trying different cruise companies if we see something tempting either in a nice itinerary or new exciting ship. Princess Cruises are very good and we have been on both Dawn and Diamond Princess which were both excellent but don't let it stop you trying others. Happy cruising.
Cruise lines do as much or as little as they need to in order to keep your loyalty, you can want all you like but unless it suits them you'll keep having a wish list.
By giving agents an extra discount to use it is just a way of spreading their marketing net wider and therefore although it costs them more the returns are better, it's common business acumen. .... Neil.