However, these projects can be useful: Enigma@home [...] does so cleverly - using a hill climbing algorithm to reduce the number of decryption attempts needed.

Using useful hill climbing algorithm (mixed with brute force method, BTW) doesn't make the project useful. Using brute force method is not a valid argument for de-listing either, if no better method is known.

Further, the Enigma messages have historical significance

I struggle to find usefulness in just being interesting from historical point of view. Also, there are thousands WWII mysteries nobody tries to solve due high cost and no usefulness.

Enigma messages have historical significance, whereas the Moo! Wrapper message does not.

While hidden message itself most likely has no historical significance, some may argue Moo! Wrapper project has historical significance in computer and encryption history.

Does (enigma@home) decoded message you describe here add anything significant to the knowledge already gathered in the books? No.

On the side note - a strong argument for why to de-list Moo! Wrapper I have described here