See, in this very interesting interview (http://www.npr.org/blogs/deceptivecadence/2012/03/16/148769794/why-i-hate-the-goldberg-variations) Jeremy Denk has the following to say:
The piece is eighty minutes long, and mostly in G major. Just think about that for a minute. Then (without a bathroom break) think very similar thoughts for 79 more minutes, winding around the same basic themes, and then you will have some idea of what it's like to experience—you might even say survive—the Goldbergs. Let's not delude ourselves. No amount of artistry and inspiration (sorry Glenn, not even you) can make you forget that you are hearing 80 minutes of G major; it's like trying not to notice Mount Everest. Not only is it G major, but it is always, (nauseatingly?) the same sequence of harmonies within G major. This is more than a compositional roadblock; it's essentially a recipe for monotony and failure. The Goldbergs are a fool's errand attempted by the greatest genius of all time.
While this had the effect of cracking me up at first, it then got me thinking: were the Goldbergs meant to played all in one go?
I mean, if Jeremy Denk gets bored with 80 minutes of G major, surely Count Kaiserling for whom the variations were written would have gotten bored too.
I strongly suspect this is not the case, but the fact that pianists like Denk do play them as a single performance piece (which is not necessarily the case with other works, even when they are more varied) makes me wonder.