Stayed in KK back in June. Dove with Absolute Scuba and it was probably the best dive shop I ever dove with anywhere. $50 three boat dives wth lunch that is huge. They lugged and cleaned all my gear. The operation was great only my buddy the dm and me in the water, the reefs were in excellent shape, wild life was outstanding, some of the best diving I have done. The DM's were also great, slow easy pace, knew the sites well. All around great time. Dove with them 2 days.
As far as KK there is some nightlife if you want to call it that around the waterfront in town just past the market. I ate at numerous mom and pop restaurants around the city and the food was great. Fried fish, soup vegies, all fresh and very cheap, two of ate like kings for like $10 US. The is a nicer pricier seafood restaurant on the water front where the food was outstanding, expensive for there but really good, you pick all your own food. KK is a small town but nice and very laid back. Hotels are either really old or new and on the pricey side. You can get a run down place on the cheap though just got to look for them. Taxis are also inexpensive.
Have a good time there.