I think "solving problems" is fine because for the most part that will be why people will use what you built. But I'm with you on "changing the world". When I hear about wannabe entrepreneurs who say they are out to change the world with their photo-sharing app ("we're gonna change the way people share and communicate with their close friends!"), in a way I'm impressed by the dedication and motivation, but wonder if they're just saying that to appear confident and motivated or if they're just delusional.

Someone was telling me that they were working on something that could become a fundamentally new mean of communication comparable to emails or SMSs. I later worked on said product and it was of course nowhere near the hype (though still cool).