(follow up to what I posted there)
Yeah, I pretty much agree with your approach. As you pointed out, I treat Muto differently.
In my eyes, Parma doesn't suppress the magic itself, it suppresses the effects the magic would have on you, and only those. But that doesn't mean it restores those properties the object had in its original form.
It is a ReVi breakthrough (q.v. Aegis of the Hearth -- no Perdo requisite) that effectively acts as a Pe Whatever on those properties that have been magically affected.
But since it doesn't actually suppress the spell itself, the properties of the target that have been overriden by the magic are not restored (though you may wish to make a distinction between enhanced and overriden): the not-pebble doesn't act as a boulder, the not-milk isn't poisonous.
Edit -- I also don't agree with Creo producing mundane objects, unless they are made permanent. Hitting a magus with a Sun-duration sword will have no effect unless the Creo effect penetrates.