So is it in fact the case that "ornament" as a verb was monstrous because "ornate" already existed as a verb?

Is the interesting thing about these words simply that they don't appear to have been verbed in the 'normal' way - i.e. by an apparent change in the spelling? After all, it presumably doesn't count in the noun-to-verb category to include the verb "to shelve" since it isn't "to shelf", whereas "to tree" involves no spelling change (although I think some linguists would argue there is a morphological change by virtue of the change of use). In these non-spelling-change cases, it's presumably for some other reason that they appear the same when verbed... You can verb "thick" by spelling it "thicken", whereas "thin" doesn't lend itself to being spelt "thinnen".

(That said, I don't think it would break any intuitive rules of morphology to have "righten" and "wrongen").

[Non-adjective verbings] Saki has an instance of the verb "to sky", meaning the practice of putting the paintings of lesser artists higher up on the gallery wall, above better-regarded work.

Nounish verbings: beach, ship, dog, horse, house, caravan, cup, motor, earwig. "Some to think of it," he umbrella'd, "there aren't many words you can't slip in as a substitute for 'said'."