Hey, I'm the dev of Cosmoteer. I can confirm you are correct, I'm trying to get feedback, bug reports, and to build a community before switching to paid. In the meantime, thanks for playing!
I'd happily chuck $10 at something like this.
Just be transparent about where you are and what your plans are.
That said, it may be hard to switch now without garnering those negative reviews you are talking about.
Even if that is just in the sense of "right, current version is the demo from now on, and all future versions are the paid version"
I suggest you gate some key upcoming features and hold on to those until you have a few to "launch" into paid mode.