I am an artist, too (musician/writer) and I have found that aikido fuels my creativity by allowing me to empty out and fall back into the present moment. This experience on the mat has gradually begun to permeate all areas of my life, increasing flow and expressiveness in my other 'arts'.
I have personally come to believe that 'boredom' is a choice, and for me arises when I lose my connection with what I'm doing, whether it's aikido or another creative project. This usually happens when I'm too busy in life or stuck in my head thinking too much.
The quick fix for me is to turn frustration into fascination by, say, counting freckles on my partners face or putting my attention on the vibration of the guitar against my chest.
This has the effect of taking myself out of myself (did I really just write that?) and re-emerging into the world more fully engaged.
Ipso-presto, boredom gone!
As far as completing long term projects (like writing a novel) remember that "It is not the water that wears down the stone but the unceasing relentlessness of the individual drops."