Yes, it's not insignificant at all. However, I hope they've learned a PR lesson here. The world is watching this mission, and hangs on every word they drop.
From the scientist's perspective, it is one for the history books, so I don't think he was speaking in hyperbole. I think the problem is that most people will never actually read a history book (beyond college), and thus, they don't have a good perspective on what's historical. Launching a robot to another planet to analyze chemistry is amazing feat; reporting that it worked would be enough to make it a historical mission, let alone that it actually discovered anything interesting. In the future, hopefully these types of missions will be routine; if so, they will all credit Spirit, Opportunity and Curiosity (among others).
I would imagine that some people got a stern talking too regarding the "one for the history books" comment. That said, I also imagine that it has helped more than hurt. We've all been talking and writing about it and wouldn't have to the same degree had the statement not been made. Even now there will be follow up interviews from major outlets only because of the statement. It's a dangerous card to play, and though I don't think it was intentional, they played it well imo. Now they've got our full attention and we all wait with great anticipation for new findings. Interesting times we live in, for sure.