Appoggiaturas: Some or All of the Time in Mozart Recits?

A huge congratulations to Erika Reiman of Hamilton for starting Hammermusik. You may already know Erica from her music and knitting blog PianoKnits. Her second Hammermusik article is of particular interest to anyone that deals with the Mozart operas: Appoggiaturas in Mozart's recitatives: to add or not to add?

On a search to justify the traditional practice of adding appoggiaturas some but not all of the time in Mozart recits, Erica discovers that there is only one scholarly article that justifies this (by Frederick Neumann), which was thoroughly debunked by Will Crutchfield in 1989. 

Which is more correct--the weight of Mozartian operatic tradition or authentic performance practice? What should coaches recommend to singers? What should singers do in auditions, bearing in mind that only a small minority of musical directors may subscribe to (or even know about) current scholarly thought on appoggiatura frequency?