I wouldn't say 'but not too much'. In my opinion, if you are trying to get into a top tier school, there's going to have to be something on your application that makes you out to be a rock star. Everyone who applies has good grades, good test scores, undergrad research experience, a good personal statement and good recommendations. One of those things is going to have to make you stand out of the crowd to ensure your acceptance.
Make sure that one part of the application is stellar, and that none of the parts are bad. If you have a really crappy personal statement, that will stand out in the wrong way. Personally, I think the largest part of the application is an outstanding recommendation, particularly if it comes from an alumnus of the school.