I've been to many trade fairs, for manufactures and distributors, and have walked literally for days looking for products that fit my objectives. I have also been to trade shows where the buyer fills out a form of things that are of interest and that list is matched to the vendors that have those products and the vendor/seller goes to the buyer. Both methods work, but in either case the buyer usually knows what their looking for. Sometimes their supprised to find something they hadn't expected, but usually there is so much material to go through that one becomes fatigued...
I have turned off the feature that allows visitors to search outside of my material, only to keep them at my site. I believe the original intent here was to provide photographers a place to host and sell images on a one-on-one basis, not a collective store front with images from many sources, I may be wrong. Keywording does a pretty good job for the basics, a search for "Yosemite" would turn up and endless selections, but searching for "Alpine Flowers in Snow" might prove more difficult. I would guess that most of the images sold here are by invitation and are of sports, weddings or other types of events... I think your idea wouldn't diminish the experience and might even provide for interesting requests...
zeph