I'm glad you're still doing well. I envy your position; I've always wanted to work on a single piece of software of my own.
I built a few things while working for startups but nothing stuck. Now I build lots of software in a nice secure corporate environment. I mostly get to do what I want and how I want it but ultimately it's not mine.
It is exactly that reasonable mix -- it's why I've stayed for as long as I have. Previously I was a contractor and so ran my own business I remember the negatives of that sort of thing.
Some of the things I've built could be entire businesses on their own and it feels like a lot of missed opportunities.