I personally have never been overly impressed with the seats on the aircraft they use for this flight but they are for sure better than Y. I have not taken this specific flight so I cant speak of the meal service but I think it is a toss up as to if I would pay the additional bucks. I am guessing your flight will actually be more like 3 hours and that is pretty short to me. I would like to add that it is likely this flight will be full since it is the only one so C may come in handy for that reason as well as getting to immigration quicker. You will be treated well in Thai C but I think 400 is a little more than I would personally pay.