"Put it this way... you can sound like James Taylor with a guitar only. Or you can sound like that PLUS him and his full band on other songs if you add at least drums/bass lines. What gets more gigs?"

Being able to do both!!! And when you are booking a gig, find out what the expectations are, what kind of audience, etc. and then decide what you think might be most suitable.... AND ... if it's not working on the gig, change what you are doing ...
As for the kb vs, guitar synth, I had lost the fact that you would be playing the keys as well ... in that case, the kb on stage will be very suitable, and when you switch will show that you are multi talented ... and the kb still gives you the option of adding as much or little accompaniment as you need/want.
t.