The entire spectrum of the Hoby has changed over the past 50 years that I have been old enough to understand it.
To begin with, the major reason why Model-A prices are falling is because the quality of the average Model-A being sold is absolute junk that is going to require major amounts of work/money to make them safe & reliable again. It's a simple explanation of the 'why' the value has dropped.
Secondly, most museums are a way for someone to 'hide money' because the owner can establish a 501C3 non-profit and create a way to travel with their vehicles, pay themselves as a curator, and access other non-profit entities to trade vehicles that could otherwise never be purchased. Vehicles in the collection can be sold along the way to 'maintain' and fund the collection's overhead. Once the time has come, the vehicles can be sold or donated. So a museum closure means nothing with regard to the overall hobby.
Thirdly, as I stated above, things in this hobby have changed. I have said it before, but 50 years ago, an average of the club's demographics was that 90% of the members restored their own car, and 10% purchased their Model-A restored or they paid to have it restored. That number is different today where 90% of Model-A owners generally pay to have the work done. The younger generation understands (-and accepts) the fact that a professional Model-A mechanic charges $100+ per hour for their services. They also embrace the fact that they must transport their vehicle to/from that shop which could be several hundred up to several thousand miles away. We all should realize that the older we get, there are more & more things that we think that we can do, -but likely shouldn't. It doesn't just refer to Model-As either. Cleaning gutters on ladders t our ages is a great example.