You assume that everyone works on their own projects. In that case, yes, you should probably market it, if nobody knows about your project it doesn't matter.

I was more thinking about contributing to other projects. What incentive do I have for fixing an issue in someone elses repo?

With this sponsorship model, the benefits will only go to the dev whose name is on the repo.

It's going to be very hard to market yourself as the guy who fixes random issues in a bunch of unrelated projects.