Some hope for those spoiled. Studies have found that spoilers don't diminish the enjoyment of a story, and may even increase it.
http://ucsdnews.ucsd.edu/archive/newsrel/soc/2011_08spoilers.asp
It's why we watch Romeo & Juliet again, even though we know they are going to die by the end (hell, even Shakespeare tells you they'll die right at the beginning: "From forth the fatal loins of these two foes / A pair of star-cross'd lovers take their life").
Unfortunately for us spoiled, we can never know if we would have been better off not knowing about the Red and Purple Weddings, as we can only experience them once. I was spoiled for both, and while I knew it was coming, but I loved the tension and building dread of the Red Wedding, and the amazing writing of the whole of Joffrey's wedding feast. There were also parts that are different from the book that no one was expecting, which means no one can fully say what happens in the TV series.