Not sure why you'd want to go. A friend of mine was in Malaysia two years running whilst the GP was on. The first year he went to the GP, the second year he had tickets but a dodgy gut and stayed in his hotel room. He said he wasn't going to actually go to a GP again because he saw a lot more watching in his hotel.
The same reason you'd go to any live sport really, for the atmosphere and getting to see it in person. I wouldn't go to every race but I've been to Spa a few times (not last year thankfully!) and never regretted it. Seeing F1 cars rattling through Eau Rouge or Blanchimont is the most amazing experience, TV doesn't really communicate the speeds involved.