"....but this is on valentines (i know, not a big thing in asia) so a cause to splurge."

I beg to differ. Valentines Day is HUGE in Bangkok!!! Just try getting a dinner res at one of the best restaurants that evening!

If you want night markets/night life during your layovers I would stay in Sukhumvit around Asok. There is a nice Sofitel or Sheraton Grand Sukhumvit. Both are short walk from Asok sky train station for the airport link, if you don't have much luggage (you must navigate stairs and uneven sidewalks).

Getting to the airport by taxi will be just slightly longer from Sofitel because it is on the "wrong" side of Sukhumvit and the taxi driver must drive down busy Sukhumvit to do a (legal) Uturn to be heading in the right direction to get on the tollway to the airport. Sheraton is on the "right" side of Sukhumvit.