Michael,
The horse is already out of the barn. LOL! Can't stop it now.
For my own interests, I've decided to use the 2 free models that I've uploaded for research and analysis.
One, a big fat, but stupidly simple, model that no game developer in his right mind would want gets downloaded a lot. So, I know that the 'freeloaders' of my models aren't likely seasoned game developers or even skilled modelers. I don't think they're the sort of shopper we're interested in. They're just bargain hunters and they might do digital art or play around in modeling software.
The second model is just an ottoman for a chair I sell. I could have put the ottoman in with the chair and sold them as a set. Instead, I'm using the FREE ottoman to see if I can get exposure for the chair with a link back to its product page. Also, the promo image for the ottoman shows the chair highlighted with the ottoman a bit in the shadows, but there's an inset of the ottoman to make it clear what is being offered. I am seeing some results from this little trick. I have 2 chairs in the furniture category and they're similar, both being antique replicas. I noticed with the first one that the category doesn't have as much traffic as the exterior architecture category, which is why I tried this. My finding are that the second chair has received as many views as the first in half the time, which does suggest the link back drives traffic.
I can also compare traffic to the free ottoman and the priced chair. The promo images are virtually the same and would have the same attractiveness in a category listing. However, the ottoman will show up with a FREE model filter and the chair won't. Well, the viewer counts are 116 for the ottoman and 27 for the chair. Since the first chair and a boardroom table in the furniture category have that number of hits over double the time, only half of the hits on the chair can be attributed to the link back. So, we'll say the link back might contribute about 12% more organic traffic for the chair.
Now, out of the 116 views for the ottoman, there have only been 6 downloads. And that tells me that the promo image, including the chair, has attracted the views. If the chair was free, chances are it would have been downloaded 116 times. Now that I know it, I might use this strategy to promote the 'Make an Offer' process on priced models when I add a back link to them in free model descriptions.
I also put a link back to the ottoman in the chair description. Hopefully this generates 'goodwill' impressions, which is what the FREE model objective is supposed to be. It surely isn't intended to be a liquidation clearinghouse service, which is what it is often used for and everybody and his brother knows it.
Many sites seem to end up going overboard with the free stuff promos. In the end the sites lose revenue, but gain a reputation with bargain hunters. When the cost to serve exceeds the return on investment, the general rule is to stop serving. That could mean bankruptcy or it could mean price restructuring. I suppose the easiest solution here might be to put a minimum price ($7) on all free models. That would not reduce the traffic of paying customers. Add a seasonal 'FREE STUFF' day or week for models that designers designate for the purpose and the bargain hunter traffic can be managed, observed and analyzed. If they're registered, they can be emailed notices of special discounts and sales. That's all up to the site admins, for the most part. But, even individual designers can begin direct marketing to their 'freeloaders'. Just use their contact button to send them updates on new models.
So, you can lead a horse to water, but you cannot make him drink? Maybe, just maybe you can!