Would definitely schedule time in for Grand Place, a good Belgian waffle, and of the many good restaurants in Brussels.
There are many hotels in the area between the train station and the Grand Place. I have found the hotels there via PL to be reasonable priced and in decent locations.
If you going up to the Hague, I would also try to schedule some time in at the Mauritshuis and MC Escher in Het Peleis as well.