Taking a boat to the inner canals was the highlight of the trip, in my opinion, especially when we swapped our motor boat for a smaller canoe, which a lady was rowing for us... a very scenic little trip that brought us a bit closer to the real life of the delta inhabitants.
They made us stop for fruits, tea and traditional music in a "restaurant" along a canal... while not being fond of traditional vietnamese songs, it was an OK stop... but if they had not stopped I would have been equally happy, perhaps even more.
What I found extraordinary is that people live where I thought no one would live... in the middle of nowhere, in canals which looked almost hidden away from the larger branches of the river, and that I thought impassable.
By renting a private boat, you can see what you want rather than going straight from one tourist trap to another. You are also on your own schedule, so there is no rush from place to place. We paid too much for our boat trip, I think -- but the privacy and flexibility made it worth it.