There's a small chance Span plays himself out of the position, but it's less than ideal to have Werth lead off. Your two options at that point are wasting Werth's power a couple times a game because he's coming up after the pitcher, or getting all La Russa about it and batting the pitcher 8th and Span 9th, which forces Desmond/Espinosa/Ramos into the 5/6/7 slots - again, not ideal.
Batting Span 8th isn't even an option in an NL lineup....you may as well not have gotten him if you're going to waste his best attribute at the plate (getting on base) by batting him in front of the pitcher a couple times.