Raynor, are you actually Christopher Tolkien?
You are an amazing source of Tolkien lore, sir. Thanks for all of your clarifications.
Lal, I like your basic psychology that Melkor and Sauron chose fair forms in order to manipulate Elves and Men.
What seems to be pulling together is that a Vala is quite powerful and free before taking a Hroa, has limits (of course) while "wearing" that Hroa, and should the Vala in question become evil, and loose the Hroa through death, becomes far weaker than with the Hroa. Conversely, a Vala who (like Gandalf) does a self-sacrificial act of good, if the Hroa dies, may revert to whatever state Eru deems most useful to Eru's purpose.