Does it really matter? It's up to you.
Here is another picture of my canoe from last summer -- same canoe and same paint job as in the earlier pictures above where the paint job does not look so bad. But because of the light in this picture, you can readily see the cracks in the old paint. It is apparent that even with new paint, the surface is not cosmetically perfect. I had spent maybe a half-hour of sanding by hand before applying two coats of paint. But the new paint itself is not cracked, and there is no water leaking through the paint. So feathering out the old crack edges is not functionally necessary.
The canoe was used several times last summer, and was paddled in two different bogs on two different days this past weekend. The second picture was taken on Friday at the put-in on the Passadumkeag River, Maine, after paddling several hours through the adjacent Cold Stream bog, cracks present, but not visible. The third picture was taken on Sunday, when putting into the West Shirley Bog in Maine. Again, because of lighting, the old paint cracks are apparent. But parked on the side of the road in Monson while enjoying music and barbeque, the cracks are not apparent and not an issue (4th and 5th pics). Indeed, one of the people listening to the music who had commented favorably on the canoe asked if it was being used, or was just being displayed somewhere. (By the way, the music was provided by guide and paddle maker and WCHA member Alexandra Conover on the accordian and friends.)
I would guess that if you've spent an hour with a r/o sander, your canoe already has a smoother surface than mine, and there is certainly nothing wrong with going for better (I appreciate a really fine paint job on a canoe as much as anyone -- I just don't want to do the work on this canoe at this time) -- depends on how much effort you want to put in and how long it may be before you redo the canvas.
