As a native Finn I can say with fairly good confidence that learning Finnish is probably not worth it unless
a) you are one of those rare people who like to learn a language just for the language itself (unlike these weeaboos for whom learning Japanese might actually have some use value), or
b) you plan to move here permanently (you can get by just fine with English even if you live here for several years, but knowing the language is required for citizenship, and it's certainly good to know the language for social reasons if you plan to live here the rest of your life)
As for Kalevala, I don't recall ever meeting anyone who actually has read the work completely. I mean I'm sure it's a fantastic work, but we don't have to read it for school or anything, so it's obviously not thought of as such an important thing by the authorities.