Yes. You are right. It should be piita, not pitta. But what I consider to be a more likely meaning of the word would not change, because piitala/pittala continues to exist in slightly different forms in modern Indo-Aryan languages in the sense  'brass'. So does taamra in forms such as taamba/taambaa. Furthermore, if the idea ' leaf" were to be conveyed, a Skt author would have naturally thought of words such as suvar.na-patra or kanaka-patra. They indeed are used in modern Indian languages as they are or in slightly different forms. 

You write: >it is not wild speculation to suppose that in the sphere of more popular discourse, uneducated as most were in the details of alchemy, the idea circulated that alchemists magically transmuted base metal into gold using rasa, and thus the word vedha used in a non-technical sense would mean "transmute", even if technically speaking it is in error.<

Researchers are frequently tempted to rationalize as they feel a need to reconcile different strands of evidence. Sometimes it is also useful to mention possibilities of reconciliation for the benefit of future research. However, rationalization should not be allowed to take the place of reason or evidence. 

Your write further: >I see evidence for this hypothesis in BCA 1.10<. 

You will be justified in seeing the Bodhi-caryaavataara verse this way only if the Tibetan cited by Prof. Kapstein ("It is the finest transformer because it causes very great transformation") is an explanation of only vedhaniiyam or atiiva vedhaniiyam and not a capturing of the import of the whole of 'rasa-raajam atiiva vedhaniiyam. As it stands, the Tibetan seems to be doing the  latter with focus on rasa-raaja. 

Now I must indeed return to my other 'time-is-of the-essence' kind of commitments.

a.a.