I play piano and organ with equal facility, and also play electronic keyboards and the harmonium. I have played guitar in the past, and have made semi-serious efforts with several semi-serious instruments, like banjo, harmonica, recorder, and tin whistle. I also played accordion for a brief time.
A degree of piano proficiency is useful for those who pursue mastery in another instrument, because piano is such a useful instrument for rehearsal, composition, and accompaniment. The converse isn't necessarily true. If your musical goal is mastery of the piano, and you are well along towards achieving that goal, there is little purpose in learning, say, the clarinet.
Most of my experimentation with non-keyboard instruments occured some years ago, before reasonable electronic pianos were on the market, and when I was working and living in a situation where it wasn't practical to have a piano available. Now that I'm beyond that, I sometimes experiment with other instruments out of novelty and curiousity, but I limit my serious playing to piano and organ.