I would say in the region of around 150 free seats are provided now in the departure lounge that are not associated with food and drink outlets. In fact it might not even be that many.
Luton's old departure lounge back in the 80's used to be a green and pleasant land for that Southend experience but then it had only had one small newsagent and no duty free shop. It did allow the airport to provide more seats than it does now in the new terminal departure lounge.
1985
Same lounge but taken in 2016 from the far end of the first photo but looking back in the opposite direction after a mezzanine floor was added to the old departure lounge in the 90's. The carpet has been replaced by a laminate floor but if you know where to look there are still plenty of empty seats on two levels as I headed for gates 1-7. I took this photo at 6:52 in the morning, just a 5 minute walk away it was heaving.