@engineer,
The logged in members don't really generate any ad revenue (probably about $30/month) so it could grow by orders of magnitude without even covering server costs or becoming something strategically relevant. I just don't see loyalty for themes being much of a factor at all, and even if it tripled our loyalty that would likely represent less than a dollar a day in ad revenue.
Plenty of other sites offer free themes and skins, I am not worried about losing members to other sites over it because nobody is gonna come here for the themes, no matter how good they are. They come here for the content and not the presentation so finding a better deal elsewhere on themes wouldn't really make anyone switch because that isn't really what they are in the market for when selecting a forum.
But in that loyalty vein, it would then be something we could give away to the core members which would possibly generate more said loyalty than giving it to all for free. But either way, because of the generally non-existent ad revenue from logged in users (which is normal banner blindness) we can put away our loyalty calculators, it won't make any real financial difference either way.
So ultimately it's just about offering them for sale and probably making around $30-$50/month on that tops (which I'd use to make more of them or improving on them), or offering them for free, and probably just making fewer themes (I'd probably just pay for a few initially and then add making more to the to do list for one day).