remember in the kempinski you have to pay your food while in the lounge it is free -- of course you cannot compare it but you wont starve as well. also i hate leaving the airport, taking taxis/shuttles etc so finally you will only be four hours in the hotel ...
the lounges are really not THAT bad.
also working is pretting good there because of the WLAN.
maybe you can also standy by for an earlier flight to your destination?
why not take a look at the loungs first at arrival and then decide if you leave the area and go to the Kempinski? No problem to cancel the Kempi by phone from the lounge if you decide not to go there.