As a developer, I use a lot of open source. But I haven't paid for a desktop application in years. The web, with it's promise of a free browser and free web applications, has done as much to destroy the perceived value of software.
Similarly, pro bono work does not cheapen the value of a lawyer work. Working for $1 per hour does.
I am paying for the updates is how I see it. As long as people keep paying, they ought to keep working on it. The minute that stops seeming to be true, I will probably switch to other products.
As a developer I have bought many pieces of software to make my work easier: Git Tower, Kaleidoscope, PaintCode, Dash, Reveal, Charles, Acorn, Paw, are what come to mind right now. I perceive all of these tools' value to be high.