We have just returned from a cruise on this ship around the canaries. We prefer to be inside and lower down because the vibration and turbulance is much less noticable there. We met some people from the higher decks who complained bitterly about noise and vibration and who felt very seasick particularly on one night of the cruise and the day at sea. We feel that unless you are wanting to isolate yourself the extra expense is not worth it, there are plenty of quiet areas around the ship and the cabins are quite adequate. It might be worth paying extra to select your cabin as you can ensure that it is not next to the lift or near (or under) a noisy area. Some people with windows/portholes on lower decks disliked the sea splashing against their window and found it unerving. Hope this helps.
We have had a de luxe cabin on the promenade deck twice on Celebration and it was perfectly adequate, spacious with a bath and shower, also a fridge and it was nice just to nip out and sit on the promenade deck (nearest thing to a balcony on this ship!!) we were just forward of the lifts and werent bothered by vibration at all. Also you will find that the Red Sea is alot calmer than the Atlantic Ocean around the Canaries so although it can be a bit choppy in the Red Sea it is nothing to worry about!! We've done it three times!!
Celebration had a 2 week refit in Falmouth in November. I understand it was mainly a 25 year MOT, plus some new soft furnishings eg carpets in public areas. Another report mentioned they were repainting the swimming pool.