Whenever a war goes the other way a new group of people would take charge and make decisions, if the Republicans had won the war then they would have made several different decisions that they thought were best and they probably would have been aimed at improving the quality of life for the Spanish.
I have my doubts a Republican victory in the Spanish Civil War would have improved lives in the 20th century. The time between the war and the 20th century is vast and the changes across the globe were vast. Given the circumstances, especially all of the changes, I have my doubt that it would have made a large difference.
At the time of the Spanish civil war Europe was in crisis and almost every nation had the potential to erupt into political violence. Spain was heavily in debt and it's economy was in turmoil. Had the Republican forces won the civil war it is likely they would have used democracy to increase Spain's debt to other nations, which would have worsened the economy dramatically over time and therefore led to a lower standard of living for the Spanish population as a whole.
It seems as though a Republican victory may have had little impact on Spanish lives in the 20th century. Most policy in those days was domestic focused, and to think that a huge foreign policy shift would have been made might be a stretch. Small changes may have been made, but they could go either way.
I do not believe that a Republican victory in the Spanish Civil War would have benefited Spanish lives in the 20th century. I think that there were a lot more issues involved than the basic result of a war. I think that the problems occurred due to there being problems even before the war.