The reason I believe that you should seal your wall is because it is a waterbased product on your walls ....now you want to use another waterbased product to wash over it....this I would think would weaken the product on the wall...it is only water and sand and drywall mixture.
I worked in the paint dept at Sears for a while ...and people wanted to use water base over there stucco ceilings.....but it created lots of problems....you need to apply an oil sealer/primer over the water based product. Try Binns....its terrific for hiding water stains and whatever...its a little more expensive...but well worth what you get!!
Good Luck.....i know I'm probably too late!!