I can definitely see the utility in working on these type of problems: a list of exercises to work through when learning a new language, or most of all, improving your problem solving skills.
Sometimes I wonder though, why do some people enjoy working on (solved) challenging problems -- rather than tackling something novel?
You can compare the actual algorithms and ways to approach the problem, of course, and they can be very varied, so you end up learning a thing or two. And the languages themselves, you can see their strengths and weaknesses in particular areas. It stimulates curiosity and opening your mind to new ways of doing things. I think that's important and valuable because when you think about it, there aren't that many opportunities to do so.
Also, when you're tackling something novel, it seems to me you're going to restrict yourself pretty early to tools you already know, and you're not going to try radically new things once you're into it because the penalty would be too high (I may be wrong though).