Is "Amadeus" a play about consumption? How and by what are Salieri and Mozart consumed?
I think you could call it a play about consumption, or at least consider that one of the themes.
Salieri is consumed with destroying Mozart. He is jealous of Mozart's ability as a child prodigy and watches Mozart grow as a flamboyant, immature, but extremely talented musician. Mozart's ability to court a lady that is one of Salieri's students only further fans the flame of his envy of Mozart.
Mozart on the other hand, is consumed with having a good time. Even though he will work extremely hard, he drinks merrily, plays hard, dresses vainly, and socializes to the extreme. He also has a great desire to please his father even after his father is long gone. Mozart died at the age of 35 and the way the play is written suggests that his lifestyle which was of great financial and health expenditure helped lead to that death.
I think that Schaffer's work can be about many elements. Consumption could certainly be a part of this. Mozart is consumed with his music. The fact that he is depicted as pursuing this ideal of artistic perfection through his composition would be a part of it. The idea of music remaining in his mind, and being able to transmit it without any drafts, but rather in perfect and pristine condition is something that drives him and consumes him. This is checked by Salieri's envy of Mozart's talent that consumes him. Between both of them is a rather interesting relationship that can be argued is formed by consumption in that both are consumed with music. Mozart's consumption is rather singular, while Salieri's is both about music and Mozart's talent, along with his lack of it, regarding it.