You assume Mugabe actually cares about the Zimbabwean people or that he has a long-term vision. The country has fallen into disrepair since he gained power, with an inflation rate fast approaching 1,500,000%. It's jaw dropping. It will continue to fall into this economic abyss until someone better than him comes along, which quite frankly makes the future bleak. Even given the impossible scenario of all the great western politicians and economists taking over the country's government I think it would be very difficult to reverse the damage done by ZANU-PF.
So why does he carry on doing the job at all? It would seem he profits nicely from it, living a life of luxury compared to his citizens, his cohorts much the same (just look at the illegally obtained 3,500 acre farm his vice president, Joyce Mujuru, lives on). For him and his party things are pretty peachy, at least if he remains within the borders of Zimbabwe.