Obviously I can only speak for myself, but here's my opinion on the effect of a writeup (for anime at least):
It's grossly overshadowed by visuals. Whether that's fantastic box art, promotional images, etc, if you ace that, you could have gibberish written in Klingon for your writeup and it wouldn't matter.
Shallow and cynical? Yes. But, life often is.
I'm not saying a writeup has no effect on individual A, B, or C, but that I suspect those individuals it actually effects are outliers. Writing a smashing writeup can't hurt, but the chances it's going to be primarily responsible for audiences flocking to your anime are, imo, virtually nil.
Smashing anime successes like Bleach and Naruto, I'm fairly certain, don't rely on the written word to captivate their legions of western fans. ;D