Back then, I agree it wouldnt have brought people to where the wanted/needed to go. But with the explosive growth that is due to take place along the waterfront (around Yonge St, the Portlands, and even more growth in Humber Bay), I guarantee you that a ferry would be very popular. Realistically speaking, ridership wouldnt really be significant until most of the development around those areas are close to completion.
During the winter time I concur that they probably wouldnt be very reliable; but on the other hand when is the bus, streetcar, and subway ever reliable in the winter?