The lounge in STR is very small and basic with nothing in the way of food other than biscuits, crisps and nuts. it is also shared with Air Berlin and gets very busy at points of the late afternoon / evening. it is in no way a place to spend any more than 30 mins in as there is nothing to do and certainly not 4 hrs.
There is a hotel 200 mtrs from the airport (Wyndham Stuttgart Airport Messe) which would perhaps be a better place to have a drink / lunch and spend a few hrs. They may also be prepared to sell you a Day room. (worth a phone call).