It might be said that the trouble with (most) aircraft
enthusiasts is that they imagine aircraft museums are run for their personal benefit... aircraft Museums are in fact visited by a broad cross-section of society... ages, interests, sexes, social backgrounds etc Typically less than 10% is an aircraft enthusiast.
One of the challenges of running an aircraft museum (this happens to be my job) is how in the heck you keep everyone happy, because their wants and desires are so diverse.
Anyway to speak to the discussion of whether or not to let people in cockpits, we have a spectrum of opinion. At one end is the person who would like "ultimate access" - no barriers, open cockpits, heck you can even take it flying if you want... At the other end of the spectrum is the "zero access" person who would like to keep the artifact in a hermetically sealed vacuum cut off from nasty things like humidity, light and all those ugly people.
Neither end of the spectrum is wholly appropriate. In the first example, the museum is failing in its duty to care and preserve the artifact for the benefit of future generations. In the second example the museum is failing in its duty to provide access to the artifact. What is the use of having it if no-one can ever learn from it?
Most museums are trying to strike the best possible balance between what, as someone has already mentioned, are ultimately irreconcilable goals.
Anyway, as it relates to cockpits, I offer one potential way to mitigate the problem. It gives you a reasonable amount of access to the cockpit of an aeroplane that no curator in his right mind is going to let thousands of people clamber inside. It's free, and you can do it all around the world as many times as you want (but you will need QuickTime).
XP-51 cockpit