I was there in 2011 for all three days. That was the first time I ever attended such an event and it was amazing. So many Porsches and so much to see. And great folks. You are also allowed in the paddock where they are preparing the cars for the races. Lots of vendors too.
I am going back this year for all three days and booked a spot in the Premier Pit Row Suites and I am doing a parade lap(s) on Saturday.
Even if you only stop by for a day, do it. You will not be disappointed.