I play guitar mostly but also have learned some bass, piano, and mandolin for multi-tracking purposes (and because I enjoy it). If you'd like to hear some of my stuff pm me.
It occured to me that it would be awesome to get several of us together and make a concept album about breaking free from the WT.
As far as this quote: "I will never master the piano and unlike you, I wouldn't think of trying to play the bass, guitar AND the mandolin in addition to the piano with the goal of getting good at ANY of them" the fact is there are many musicians out there who are talented enough to play more than one instrument and are more than good enough at each of them to entertain the masses. Take Paul McCartney, for instance. In any given concert of his he will play bass, guitar, mandolin, piano, and ukulele. I'd say his music is fairly adequate, wouldn't you?