If you have no practical use for it, or no interest in other Slavic languages, I'd agree. Although I rarely speak it more than once or twice a week these days, I hear it every day. Now that alone makes it useful, because if some Polish pr*ck decides to call me something disrespectful in Polish, and thought I wouldn't understand, they may be surprised to find that I'm calling them an ambulance :)
Seriously though, its helped me in other languages, saved various employers a fortune on interpreters, and helped me work my way round Poland. So for me at least, it's very useful.
However, I rarely bother "learning" any more of it, because I can speak it faster than English, I'm fluent enough to engage in conversation in virtually any subject, I understand it as well as English, and i can read/write as well as I'll ever need. So even if I wanted to, I could never forget it.
I used to think it was a useless language when I was in my teens, and even stopped speaking it completely for a few years, but I changed my mind and I've never looked back :)