Hi Pedagogue,
According to Fowler's Modern English Usage, "wages" as singular is an old usage that died out in the early 18th century. And according to Partridge's Usage and Abusage, it is an archaism. We might just as well write: the wages of sinne...
It might go past unnoticed in a figurative sense because it comes after the word sin - "sin is" rather than "sin are". But I cannot think of a sentence in which "wages is" sounds correct.
My wages is too low?
Wages has not risen this year?