Once you start thinking about it in a mercenary frame of mind, then you're finished. You're a joke, because there are too many mercenaries out there already.
On acoustic guitar I tend to stay in the key of D for some reason. On electric guitar I keep basic: C, G, D, and A. The key of D minor is also real good for me.
It is all about being open and paying attention to the music in your head. I think most people have original music playing in their heads from time to time.
Around '75 when the recession hit, club owners started going to disco because it was cheaper for them to just buy a sound system than it was to hire a band.