It's very difficult to learn Russian.
I don't agree with this myth. There are many languages that are really difficult to learn. And Russian is not among them. Russian grammar is difficult but so is the grammar of English and German. If a person really wants to learn Russian language he will succeed in it. Of course it will take much time and will but if one really needs it he will do it.
Not too many people in the world speak Russian.
This myth is really only myth. If you look at the globe you'll see that Russia occupies a huge territory, so a lot of people speak Russian. Let's take in consideration ex- Soviet countries. As Russian was official language of the USSR all former soviet republics spoke (or at least could speak) Russian.
Russian is useless because Russia is a closed and dangerous country. Visitors always have problems there.
I absolutely disagree here. Russia is not a closed and not a dangerous country. It is less dangerous then some eastern countries. Many visitors come to see our places of interest every year and I think it's always better to know the language of the country where you go. So Russian can't be useless for those who come to Russia. Of cource it's not necessary to learn all the grammar and phonetics of the language, but to know some frequently used phrases can be of great help.