President Ahmadinejad often describes the nuclear program as an example of how Iran has become a powerful country. In his usual understated way, he has taken to describing Iran as the most powerful country on earth.
In his mind, the advances in the nuclear program show how Iran has the ability to do what it wishes, irrespective of complaints by outsiders, so the nuclear program has been very useful. Even when Iran does not have nuclear weapons, Iran can use this image that it's making advances on the nuclear front to argue that Iran's position should be listened to carefully, that the tide of history is with it, and that Iran has every right to voice whatever opinion it wishes in meetings such as that in Geneva the other day.