The thing that's made the biggest difference to my songwriting output seems to be making the change to self-employment. Now that I work for myself, and from home, I'm not completely exhausted after work to the point where I don't want to do anything. I have energy not only for writing songs, but for going out and playing them too, and that's made a massive difference alone.
(Since my first post in this thread, I've started writing a lot more
)