You should have a look at our live FSM view feature in Sigasi. Sigasi now has an interactive State Machine Viewer that updates while you type your code. You can also click it to navigate back to your source code. This interactivity greatly enhances the advantages you described in your post.
And it even works with unfinished or broken code.
You can watch a screencast at http://www.sigasi.com/screencast/vhdl-state-machine-diagram