I won't comment on the painted vs. varnished issues -- you know what you want, not what others want :^)))).

Having said that, snapping some covers on some handrails isn't that big an issue, though. The maintenance issues would be reduced if you (as you would) sealed the rains all around so that they didn't absorb moisture from the deck side.

Of course, the toe rails, the companionway, the dorades, etc. --- WHERE DOES IT STOP? ;^)))). When we had our Sabre, we didn't have covers for the toe rails, but almost all the other teak on the topsides hade their little "coats" of canvas. IT did really help with the durablity of those items.