I think the reason he doesnt join the fight is more personal than it is about having better things to do. Im sure what hes doing is probably very important as well, but thats probably not his reason for doing so.

Seeing as the major reason theyre going after itachi is because sasuke is now on the move, its really more about retrieving sasuke for a good portion of the konoha team.

Reread chapter 237, it compares naruto/sasuke to jiraiya/orochimaru. Jiraiya talks about how only an idiot would chase after someone who is clearly evil (which it flashbacks and shows the past where he tried to bring back oro). This being the case, I think hes more or less still a little scarred from the fact that he was never able to convince oro and also realizes that naruto needs to find out for himself exactly what kind of person sasuke is.