I disagree.
GO's fare's are too high for most and people don't use it due to this. GO ridership isn't lousy in Toronto because there is no demand but because the fares are simply to high and if you don't live right at a GO station {which the vast majority don't} then you end up paying the TTC fare as well.
People are very price sensitive, as recent studies, UPX, and common sense dictates. Ditch the DMU and replace them with 4 to 4.5 car long subway trains. They would offer higher capacity, less dwell times, and far faster exit/entry which is essential with more planned stations.