You'll probably get responses all over the spectrum of miles here. It really depends on your endurance/fitness base and how much your body can handle without breaking down.
I guess I should say I really don't have a good answer, I ended up with a peak week of around 47 miles, but I think this was on the high side of what most people did. A lot of folks did this race with a lot less miles and they also succeeded. I was just really concerned about getting in the adequate back to back runs, so I peaked with a weekend of 11 miles followed by 22 miles the next day. Probably didn't need to go that far, but I did feel pretty good through both the half and the full on race day, so I guess it worked to an extent.
Hope this helps, and I'm sure you'll also get great advice from others who have completed Goofy. Good luck training!
Steve