It would be nice to have an add-on I can generate stuff along a curve, and also, scale this stuff smaller closer to the end of the tail, its neck and bigger on its back. But maybe, that’s not the purpose of your add-on 🙂
So, you can do this (sort of, anyway), I have just failed to mention it in the documentation :-). It’s not ideal though, as the Blender API does not work as it should and I am therefore having to “fudge” this slightly.
You can set the radius of your curve points to decrease (not increase) the size of the stroke. A radius of 1.0 is 100% of your original brush size. A radius of 0.5 is 50% and so on down to 0%. As an example:

I am looking for a better way to deal with this, so it should be improved in future.
Here’s my dragon.
I can get everything to work OK with your dragon, are you still having issues with that? I tried to record a GIF but my laptop isn’t quite quick enough to do that with the high res model.
When adding points, everything else, except adding points in the viewport, is death. Clicking around everywhere I encountered this error message, doesn’t mean anything to me.
Yes, you are correct, this is just buggy at the moment. If you click outside the object it will screw up. I will make this better so that it handles the errors better.