I don't think you need to spend a weekend in Korea-- especially if they have the choice of spending their time in HK instead. You'll probably get the "feel" of the city during the weekdays. Koreans (especially in Seoul) tend to be arrogent and pretentious-- I should know as I am one. If you could spend more time there, I think it would be worthwhile because you could get past Seoul's snobby exterior-- but if you only spend a short weekend there you will probably leave unhappy.