This year, some people got an offer for 5% off if they rebooked within 2 weeks after returning from their trip. I didn't get that offer. There was also a $100 return guest discount. You can't count on anything from year to year. It's never the same.
A little insight into how few quests have to book before the price goes up...I booked our 2014 trip at the introductory price on June 1 and including the two of us there were 4 people booked. The price has gone up twice since then (it's $310 pp higher). I called this week and there are 9 guests booked. That really surprised me it had gone up that much with so few guests. I don't know if this is typical.