"Do we have contemporary writings suggesting that they were merely wage slaves rather than workers subscribing to a delusion of the age?"
We have no evidence either way, but we do have historically recorded disturbances such as The Peasants Revolt and similar uprisings in Europe to indicate that all was not sweetness and light as far as the relationship between the peasantry and the Church was not all sweetness and light.
The Church held massive power and influence in Europe - it part part of a ruling establishment headed my monarchs "chosen by God" to rule.   
To suggest that they ruled without opposition was a nonsense and to take the word of people who still don't question the authority of the church is equally so.
There has ever been a study of the relationship between the state and the people, basically because the peoples' opinions were never taken into consideration and remain unknown and probably unknowable.
You only have to examine the folk literature to see that criticism of the church and the state was deep-rooted in the peasantry - that is common to all feudal societies.
Stupid quotes out of context by believers mean nothing - "the Pisan's" would be a reference to the privileged classes in Pisa as interpreted by the church - the unnder-classes were never asked their opinion - if they were, where were they recorded?
"To the Glory of God" was an advertising slogan little different than "fabulous pink Camay", with the backing of divine authority.
Jim Carroll