Using © seems like a good idea, just on i18n grounds. Where did you see © preferred? Sounds like advice for really old browsers (using IE4, anyone?).
I question whether it's worth adding this overhead to every request. How likely is it that a design will not be refreshed for enough years to be out of date (and in such a case, an old copyright date is probably appropriate).
Finally, there's a legal argument for leaving it alone. The © date is the date of first publication, not necessarily the date of the last edit.
And a minor issue: with the server and client in different timezones, this logic will show © 2013 for as much as a day at the end of 2012. Easy enough to fix (subtract a day, or a month, from now()), but still, it seems to me that the best approach is to leave the year static and arrange so that it can be updated in one place as appropriate.