An important part of the PRI's electoral victories stems from the problems of the PAN and PRD governments. In many cases the differences between the old PRI and the opposition aren't distinguished. But the PRI also wins elections because it has a powerful machine, because it uses funds from the public budget, because they are very efficient users of clientism and territorial control, because they dominate the electoral institutions in the states where they govern. So Oaxaca with more PRI will simply be more of the same. A change of power can mean, despite all of the limitations, a relevant change so that those who have governed Oaxaca for decades don't continue to do so...That last is more circumspect than what I would write. The PAN and the PRD may or may not govern better than the PRI in Oaxaca, but power changing hands occasionally is certainly a positive development for its own sake.
Shifting directions, I think we have two primaries worries about a potential PRI return to the presidency shaking out: one is that the PRI of today will again embrace its worst practices of the past, especially regarding corruption and electoral tricks.
The other is that the development philosophy of the PRI has not matured and the country will revert to some version of the nationalistic boom-and-bust-ism of the final decades of the twentieth century. The PRI's economic stewardship, incidentally, is related to its electoral strategy, because injecting huge sums of public cash into the economy ahead of every presidential election (or at the very least, favoring short-term growth over medium-term stability) was standard practice, and led to a number of crises.