I've come across quite a few multi-instrumentalist ...but, they seem to always play one instrument better than others. They may be pretty good on the keys, and on drums .. they can play all the standard licks & grooves, but aren't exactly beastin'. You're not going to hear too many sit down at an organ and rip like Butch Woodie, then sit at a kit and play like Chris Coleman. If they do, follow them home ... no one will lives there but them, lol...
I applaud anyone with the willingness to learn more than one instrument. In my opinion, it helps you to learn to be more supportive of the music, 'cause you're not hearing things from one perspective, at that point.