... does contributing more have an effect on my results in the search?
It should only have an effect on search by Date, of course, where your new images appear first. Buyers, especially those with subscriptions, may watch the newest files for images they like.
Will contributing new images change the rank of your images in the other kinds of searches, such as Best Match? I have never heard that it can. However, none of use contributors knows exactly how the searches work, so it is not impossible that some might weight your images higher in results if you are an active contributor.