The no addiction assumption is included to make clear that the “wanting” part of your brain will not be hijacked; you will only engage in wireheading after the vacation if you make a sober choice to do so. Wanting vs. Liking summarized here:

http://lesswrong.com/lw/4yq/the_neuroscience_of_pleasure/

I agree with your prediction that a person who chooses the vacation will most likely pursue wireheading when he/she returns home.

(Best sex ever + Best joke ever + Best meal ever + Best love ever +… Best whatever ever)^(3^^^3) for a week would make quite an impression.