I'll echo sgRant's comments about the spraydeck being a welcome addition to the safety margin. I fully accept and manage the inherent risk in all activities, rather well I fancy as I've never had a really full-on scary "is this how I die?" moment despite have done plenty of trips beyond the daytrip crowd. (Touches wood with feeling.)
But I really don't want to die. Cumulative square yards of skin, gallons of blood and assorted sprains and bruises are ok by me, just not all at once, or capsized far from shore in freezing water and gear floating away.
A spraydeck just adds so much confidence in making a desired camp despite the wind coming up stronger and earlier than you expected. As well it has all the other benefits, especially the aerodynamic improvement when paddling. I think it adds a good 20% to our speed into the wind.
I still need to try out my idea of unlashing the rear half and holding it vertical with a found pole as a mast. A held rope to the tip of the spray deck over a slip arrangement so you can dump the sail in hurry onto and behind the bow person who then gathers and controls it. A spar across the gunnels to take the pull, so it's not pulling on a single lash point.
Within 45 degrees or so of downwind only, of course, a canoe hull is so far from a good starting point for a sailboat that the sailing rigs seem a little silly to me. Just get a sailing dingy if that's what you want!
When driving, the buffeting and noise are perceptibly reduced, that should mean lower drag as well but I can't verify that with measured FE. The key to rigging for transport is a rope from bow to stern outside the spraydeck, looping inside at every opening and around a thwart or seat so as to pull the spraydeck into the canoe.