This is a separate issue from whether or not you and I should learn Spanish or some other language. I have studied Spanish, German, and Russian in school.
If I went to live in a foreign country, I would expect to have to learn their language. I would not expect them to adapt to me. As a matter of fact, on two occasions when I VACATIONED in a foreign country, I spent 6 weeks (Italy) and 8 weeks (France) trying to learn the language. I listened to tapes while exercising or driving. I'd estimate about an hour a day, 4-5 days per week. I can't say I was fluent, but I could speak "restaurant" French and Italian, enough to get around, change money, order food, buy things in stores, etc. I watched a little bit of French TV and understood about 60% of what was being said. I was able to understand about 80% of what I read in the newspaper.
I expect that if I actually invested a REASONABLE amount of time, and if I were living in those countries and immersed in the language (job, friends, TV, newspapers), I could become reasonably fluent.
So, YES, I DO think it's wise to learn a foreign language. But I think it's even more wise to speak the language of the country your living in.
It takes time to learn a new language and the older, the more difficult. Of course they should learn English. Second generations learn it quickly.
oops ... that should read "you're living in"