The title of this blog; "Less Is More - Case In Point" refers to what I consider to be a pretty fair amount of downloads I have earned with a relatively small amount of images available...
Specifically: Nearly $450.00 in earnings (523 downloads) since 2005 with a mere 31 images online. Average downloads per image: 16.87
While I'm not positive that this is a great feat, it doesn't seem too shabby either. I achieved this by basically, you could say "selling out" and creating graphical images that I felt were sure to be downloaded very often, with a handful of photos thrown in for good measure. For the most part my plan has worked flawlessly.
Now I do realize that many "cliched" images have a better chance of being rejected, but I found that with a little extra effort, designing as if for a client, not just for myself, I was able to get images such as my "Happy Holidays Text Ball" and "Flatscreen TV" accepted and into Level 4 status pretty quickly.
I guess what I'm getting at is when you, the photographers or designers, are taking or preparing images, don't be afraid to cater to the mainstream and REALLY think about what people in direct mail houses and the like will be searching for. It's performed quite well for me and I can only imagine how well it would serve a contributor that has the time and resources to put together many, many images with this in mind.
Additional Quick Point:
I also download many images from Dreamstime (491 to be exact) and all too often I see great images that could be very popular if they had just been approached in a more conventional manner as opposed to overly "artsy" or abstract in nature, angle, etc. Not to discourage any creativity, but it pays to remember who your buyers are. Mainly people who want crisp, clear, and very literal images.