Sometimes, I agree, but most times - I can make a better imprompteau arrangement by playing the bass and keys together. It's like free rehersal. The 2 parts "click" and compliment each other with almost no confusion or toe-stepping.
Playing bass lines really opens up possibilities for soloists ..... the "canned" patterns get so boring after a while because they always sound the same. You NEED to add some more of yourself to the mix, and OFTEN.
I still prefer to play my right hand as if it were the whole band, and not a solo voice. Makes for a fuller sound behind my vocals, and keeps the arrangement fresh each time.