If you look at every single FT request for driving advice, there is always a post that says "Don't drive!". It's not helpful. I am very glad someone clarified Sunday traffic might not be awful.
As to the advice to arrive in Amsterdam by train, I wasn't aware this was an option from New York. Sounds exciting, but I'm going to pass.
HMV, thank you for your kind offer, I'll drop you a PM. I mentioned I have the entire rest of the day on Sunday, so the walk in Den Haag sounds great!