If you do get 1 hour or two hours free, then take it and enjoy it. But that's not what you put in your post.
Everywhere charges landing fees (oftern higher than Duxford) but I don't expect Coventry or Lydd to put on a fantastic museum for me, perhaps a fly past from a Spitfire, or just give me the special feeling of lining up on the same piece of grass that was used so well 60 years ago.
Having flow in for the Flying Legends last year with my wife and friends, being stung for a bill of over £120 was eye-watering - I would ask Duxford to think about that for this year. Also think through the logisitcs as we were all kept waiting for ages to be bussed back to the aircraft, followed by a lenghty departure queue. But the point is, without funding, Duxford wouldn't be what it is.
Your point about car parking is irrelevant - cars parks don't need fire cover, FISO's, runway inspections, or any number of other things that make a landing fee.