The thing that makes me not want to take Ashes and Dust is Murder Protege. If Murder Protege is on the table, Ashes and Dust is basically worth -3 VP.
Otherwise, strats and schemes and board topology (and let's face it, mood) determine whether I'll take it or not.
I wouldn't worry too much about Ashes and Dust feeding Nephilim grow lists. If someone surrounds Ashes and Dust with terror tots or even Young Nephilim, you'll be getting Abominations out of the deal as much as they'll be getting grow & mature.