I am at STN 3-4 times per week - and 100% agree! No matter how busy a public place gets, a half decent management team could maintain an appropriate cleaning schedule.
I think STN's terminal is the most stunning design of any airport in the UK - but build a place out of steal and glass...it's not rocket science to work out you're going to need a few window cleaners!!
The glass tunnels from the car park/station level - in fact all the glass in the place is constantly filthy!