I'm going to have to disagree with you on quite a lot of that.
Firstly, we had the wettest June on record, so they must have been well aware that the grass car parks might be a problem, so why did they not start planning for it earlier? Get some gravel, wooded planks, duck boards. Why did they only start taking action yesterday afternoon? Their contingency plan clearly wasn't very well thought out.
I also don't think you can start blaming people for poor planning. As I said myself, I go every year and I left what would usually be plenty of time for a Friday.
I personally didn't see much in the way of people abandoning their cars, I was actually quite angry when Silverstone Radio tried to suggest that today's problems were all due to that. You have to also remember that people were stuck for hours, I had breakfast at 7am and wasb't able to get any food until 5:30pm, not to mention people needed to use the toilet as well.
One aspect I especially thought was poor was the marshalling, however, that is something I've been critical of in the past, because they don't have enough of them and many are just not interested in.
When exiting the A43, there was the traffic coming from the other direction and over the bridge. Here you should have had Marshalls controlling the traffic to make sure that the traffic was coming equally from each direction. Same goes for the circuits inside the roundabout, but they had nobody.
It's also no good just saying that is a Friday issue, the fact that they are now asking 20,000 people not come and giving refunds demonstrates that they are in a critical condition and struggling to handle it. Everyone knows that they need to be there when the Car Parks open tomorrow, or not bother at all, thus its going to be crazy busy, even if you are always there on opening.