This may be something that already known, or maybe it is just a coincidence.
I have a very small number of files at Fotolia, and was only getting a single sale everyday or every other day. I stopped uploading to FT in May and my sales starting dropping off. In fact, I went two full weeks without a single sale during the first part of the July. I decided a few days ago to upload a handful of files and within two days I have had a half-dozen sales.
Is this just an odd coincidence, or does contributing more have an effect on my results in the search?