If you aren't comfortable with a train ride into the city, you can still clear immigration and enjoy the shopping on the main floor (Schiphol Plaza) of the airport. Great stroopwaffles and speculoos to be had in the Food Village supermarket. Pick up a kilo of Belgian chocolates at Leonidas. Have some terrific frites at Vlaamse Frites (don't forget the mayonaise.)

As nice as the KL lounges are, you can easily "enter" the Netherlands without leaving the airport and add some variety to your layover.