Sounds very interesting. You have been at it a long time! I only started using AutoCAD in March when I joined my current company, but always found it really easy to pick up, and, as you say, really enjoyable.
I was vaguely trained by the chap that I took over from, and read some of a book on AutoCAD, but there's nothing like actually having to work on it to learn.
I think that, unfortunately, we don't need inventor here. I am hopefully going to be learning Revit at some point as I work in building services.