I think people underestimate Selene's haste buff. Whispering dawn is pretty godlike and it's hard to give up, but last I checked, that haste actually mathed out to about equal with AST cards.

I don't really think forcing your co-healer to cast an additional AoE heal every so often really outweighs the dps potential of having a second AST essentially(or the first one I guess if your partner is a WHM).