As I have a colossal issue with a boat breaking when I am not even touching anything, we should be able to reinforce them by creating iron boats or even diamond ones [should one wish to do so]. As such the amount of 'damage' they take would be substantially higher before breaking.
I think the damage they take is a bug, not something really designed into the game. If it is a bug, then I'd rather stick with the cheap little boats until they fix it because I don't think they would have any better luck trying to program a "hardier" boat. If the current situation is by their design, I wish they'd remove it (i.e. just program the game so boats can't take damage at all).
The issue I have with them is that they are so hard to break and collect (the little boat) when you want to take them out of the water. I usually end up hitting and swimming after the darned thing halfway across my survival island map before it breaks... which almost makes it quicker just to swim everywhere I want to go. If I leave them in the water, I wind up with a bunch of derelict boats drifting around my ocean.
Like UpUpAway said, it seems more like a bug than a feature. I kinda doubt they would add ways to increase a boat's durability via crafting rather than simply just boosting it's toughness so they don't break normally.
A bit off-topic but the new PC boats introduced in a recent snapshot won't break at all unless mined and I'm pretty sure they won't even move unless occupied by a player.