When I was growing up, my parents and relatives would constantly try to convince me to learn my ethnic language, half to know my roots and half to catch the "China train".
In university, I took it upon myself to take Mandarin courses for several years, but only got to middling competency.
Now, as the years go on, I find that once innate desire to "one day learn Mandarin" gradually fade away. In terms of usefulness: - it seems less and less likely that I'll ever live in China for a significant length of time due to all the common reasons others in the thread are mentioning - I have many international Chinese friends, but our friendships are based on cultural affinity rather than linguistic affinity, so they're perfectly fine switching to English whenever we need to talk about something complex.
It's interesting, but many of my American peers of Chinese heritage are actually learning Korean or Japanese, which would have been extremely rare 10 years ago.