In most cases shipboard credit can go to gratuities. Also, for the previous poster who already purchased dining, they usually do NOT change the price after you have made a dinning, excursion, or drinks package purchase.
I originally asked the question because I have a cruise coming up in January and was thinking they might raise gratuities before then, and if they did would they give me an opportunity to pay them ahead at the old rate. That was really the only question.
Personally, I used to prefer that they build in the service cost to the price since it is something that always has to be paid however these days, I am OK if gratuities is not included since it reduces the final payment amount and therefore less money to try and get back if you cancel after final payment.