>> I'm not sure how I feel about this one.
I think this may be a case where because you have a bunch of freedoms, you feel like you should have more.
I say this to re-assure you, not critisize you.
Open Source, and Free Software, are very clear on the 4 freedoms you enjoy. You can use, modify, distribute etc.
But it's not a 2-way street. You have no rights about what goes back into the project, the author is under no obligation to receive code contributions, no obligation to add features, fix bugs, or anything like that.
Of course lots of projects actively seek out contributions, but it's certainly not a requirement - nor (IMO) should it be.
Coversely open source has struggled to find viable financial models. This sounds like a success story and we should look long and hard at any successful financial model.
So, I don't think you should feel unsure. If you want to contribute then chip in some loot. If it means the project becomes sustainable you are the big winner.
But most of all, I think, be careful of adding "more freedoms" to your understanding of OS and FS, when they don't exist.