"is one tithing dollar more sacred than another?"

I have no idea what point you're trying to make here.

"if all the metrics for two applicants fall within acceptable ranges...what differentiates one candidate from another?"

ok, so if you're talking about a tiebreaker - which isn't where this conversation started, but ok - why would you give the edge to a legacy, who has been in the church for generations, over a convert. I don't know that you should be favoring one over the other. as far as BYU's overall mission in the context of the Church's goals in building up the kingdom, i think you could make an argument for the convert.