Hi Paul,
I really appreciated your email, even through I'm far from calling this "my framework". I have been involved in TG only for the past 2-3 years and the framework evolved for nearly 10 years thanks to the work of Mark, Chris Perkins, Christoph Zwerschke, Michael, Kevin and many other people that contributed and I'm probably missing.
I totally shared your feelings when I got involved in TG, it's the framework that so far best matched the way I think and like to work and that's why I ended up contributing to it.
Regarding being unsure about where to start for contribution, my suggestion is just to go on with whatever you need yourself.
As an user you are in the best position to know what users need.
It's usually easier to start by fixing bugs and documentation as in that case you can just fix the bugs you are facing yourself or write down things you had to learn and were missing or unclear in the doc. But even publishing libraries or pluggables you wrote for yourself is a great starting point as they can be a great foundation for other people that need the same even when the lib is incomplete.
In the end, whatever you needed yourself is something that others probably need and will be appreciated :)