I think depends what kind of a theme, and how much downloads it gets. and even then it might be not even worth it. If it's a good theme, the link might stay for a long time, if it's medium quality it might be removed in a few weeks. when i track a theme with 4k downloads, with a keyword in google i.e: "Designed by Elegant WP Themes and Made free by Car Dealers" sure you see 500 results, pages... go to the last page and you will see the omitted results, then export that list of 36 uniqe domains carry the back link to a pr checking program and then most of these blogs are pr 0, with a lot of content, that can even be not related to your niche, and only few are pr3-pr4, probably 1-2 domains. with other theme i got 8k results, but omitted was about 50 domains, same case with those, most pr0 useless spam. so.. what is it for you, is theme sponsorship worth it? wont you use that money for good paid quality links? just want to hear some thoughts..
first of all any slightly tech savvy person can remove the links, secondly you want links from relevant websites, and those sites using your theme will hardly be relevant. So its not worth it.
I agree... but if the back link is to a wordpress themes site, it might be relevant after all, because the whole blog is wordpress powered... footer can be encrypted, but i think the most important thing is a quality free theme which people will use
Can be worth can be worse, But not worth it you know why because sooner or later theme gonna get old and no one gonna use the old theme so no links
If only the Theme gets popular it can be useful. But there is a problem in this. You can't control the distribution of the Theme. As it is free it can be used by anyone for any sites including porn, casino, gambling related sites and you can get bad neighborhood penalty for it, who knows?