I think you got your money's worth from the stock tire!
8,800 miles is pretty darned good for a motorcycle tire.
I wouldn't put your life at risk and keep riding on that tire any further since it's so well worn, especially as we get into wet riding season. (IMO, even if you don't ride in the rain, you never know when you might encounter some damp pavement, especially in a corner.) I would mount your new tire and enjoy riding without the worry!