I would assume that those who can heal would have a positive effect on those around them. Either their genes or memes would mean there would be more in the next generation who would be able to heal... either it would be genetic so those who can heal would be more likely to have more children who in turn have more who can heal or it would be faith based and having a visible sign of a gods power by seeing the ill regularly revived would definitly increase zeal in the area.
So population would boom and if anything the percentage of those capable of casting cure minor wounds would increase.
Now an increasing population of faithfull would also have a positive effect on the number of clerics. More faithfull would empower the faith in people and wealth. Also the cure minor wounds would mean more would survive. This is three positive feedbacks working together, more faithful, with more wealth, who are all surviving longer. More clerics leads to more powerful cures, cure disease and blindness being the most useful... since half the population can cure minor wounds. This in turn is another positive feedback mechanism... disease, famine, blindness, undead plagues would be defeated and the population would boom again and/or live significantly longer.
Longer lives would lead to more powerful specialists (more training and more time to apply it) in other fields so the quality of life would improve... it wouldn't be a medieval world... it would if anything be a better quality of life then now.