Not to make trouble or to pick on anyone...just another view, or another facet of the same situation.
IMHO you have lumped together a few examples that have very different backgrounds.
I think we would all agree that Memphis Belle is a historically significant national treasure/memorial/symbol because of its combat record. "Lacy's Lady" in Oregon (currently "flying" over garden supplies) has no combat heritage & no historical significance: "Lady" has been under private control (in private hands) since obtained from post-war surplus stock. Then, if we need another unfortunate situation of a neglected warbird, there is always "Preston's Pride" in Tulare, CA...another sad situation, but, I digress a bit.
If you want to make a more apt comparison of historically significant warbirds in "public" hands, let's look at "Memphis Belle" and "The Swoose" at NASM (the only known surviving D model Flying Fortress and one of the very few surviving American combat aircraft that saw continuous service from December 7th 1941 until the end of the war).
In a little bit of "damning with faint praise" here...The Belle, compared to The Swoose, has been more cared for and better protected since the war, perhaps ONLY by comparison to the way-too-long period of neglect suffered by The Swoose, first in LA and then later (unforgiveably IMHO) by NASM. And, in spite of its rarity & significance, no schedule for the restoration of The Swoose has been announced by NASM.
Lest you think I am just some critic of NASM, I have been member of NASM's Air & Space Society for well over a decade; contributing my money for aircraft restoration and maintenance. For the same reason, I am also a member of the Friends of the NMUSAF.
...moving on...
Adding the B36 from Fort Worth into the discussion of Memphis Belle is a little apples & oranges kind of thing. With a bit of luck, some perserverance and some connections, you can actually see over 40 surviving B17's in various conditions (I've seen 32). But, you can only see four (count 'em 4) B36's (I may be unaware of partial airframes/cockpits). Both aircraft are rare, but for rather different reasons...combat history vs. low numbers.
Your point is very well taken that there are similarities in the inability of all these groups to create working coalitions to raise sufficient funds to restore and protect these rare aircraft, so the NMUSAF decided to step in and take action to change those two situations.
And, you raise a very legitimate concern that this might possibly indicate some underlying problem with future preservation of Warbirds. I wish I knew the answers here. Since I don't, I have chosen to donate money to several entities that restore and preserve these touchstones to our history. Its not an asnwer, but I think its better than nothing and it is something I am able to do.
...over to you...