It really depends on a lot of variables.
We booked early for May/June this year, on a 2 days free offer.
But then I was looking at adding a dining plan. I priced up the total cost on the new offer of 25% off and free dining plan, and it came out as less extra to pay that the cost of adding the dining plan to my original booking.
As long as you are "upgrading" (ie paying them some more money and sticking to same arrival date) there is no penalty for cancelling and rebooking on a new deal.
So, for June next year, I have booked under the 2 days free offer (I also booked through the Irish site, and this didn't have a half term price hike!). We plan to add a dining plan. So, once the new offer comes out, I will see if it's cheaper to upgrade to the new free dining plan offer or to stick with our booking and pay for a dining plan.
