Yes, that's a good place to start. Wilson (or TR '12 if you prefer) gets involved in Mexico. Mexico loses the northern states: Baja (territory), Sonora, Chihuaha, Coahuila, Nuevo Leon, Tamaluipas, and Sinaloa and Durango would be good too. Wilson and TR are probably dumb enough to push for Zacatecas and San Luis Potosi too. Even better.
All of Zapata's rivals now have their bases in U.S. land or are discredited. The importance of eliminating the Sonorans cannot be overstated, as well as getting rid of Pancho Villa, Zapata's Northern counterpart, who was the caudillo of the North in general and Chihuaha in particular.
This is the only way to get Zapata to power really. Zapata and Villa were, more than any other figures of the Revolution, true revolutionaries interested in improving the lives of Mexicans, but they were too bloodthirsty and also bandits at heart. They were not trusted by the rest of the revolutionaries. So you'll have to get rid of the support base - literally - of the rest of the revolutionaries.
Zapata will easily come to power in the rump Mexico, and he will be bloodthirsty. But Mexico will likely be better off. Real land reform and agrarian reform will be instituted. Educational reform stands a better chance as well. Mexico did this half-heartedly before and after Cardenas because most of the leaders were Sonoran, or in the Sonoran clique. In Sonora, there was less need for land reform, so the leaders there were considerably less radical and did not understand, or care to understand, the problems of the poorer and indigenous South. The haciendas were not their concern.
Zapata has the potential to be a Mexican Tito: A tough bastard, but the best shot his country's got. I see Villa in the same light, but as long as one is in the same country, the conservative revolutionaries will use the two's divisions against them and both will lose. The conservative revolutionaries and Villa are largely gone with a Second Mexican War. And one more thing Zapata has in common with Tito is that I could see him turning to the Soviet Union for support at first, but he won't be its lapdog. Such support will be like Sun Yat-sen and the KMT: Zapata won't pledge he's an outright communist, but the two will be friends. Like all sane (this rules out Santa Anna) Mexican leaders, Zapata will try to concentrate on internal problems instead of the Colossus to the North. With the turmoil of integrating New Mexican territories and likely still being involved in WWI, he needn't worry very much.
Mexico will probably end up being in the first world, around Italy I'd say. If this is what you want, you can do with a POD in the 1970s. I think a better and different Mexico is what you want. Ironically, by losing more territory to America, Zapata can come to power and ultimately increase Mexico's standard of living. But with Mexico's luck, things could always go to hell and another civil war could occur when he dies.