For some reason Alaska cruise prices seem to never go down, so if you found one you want to do, I'd book it. If there is a price reduction, you should be able to get any savings, but I wouldn't count on that. I've always used a good cruise travel agent when booking cruises, makes it so much nicer to talk to them if there are and questions or changes that need to be made.
What ship are you looking at. I liked going round trip from Vancouver much better than from Seattle.