If I were going to dry out on beaches to
paint, scrub or
repair, I'd want keels. You can also put
tanks in keels, keeping weight low, where it is best kept. It is probably easier to make keels bullet-proof, and they will help protect the
rudder (and props if you have inboard engines,) against debris and grounding.
Kelsall doesn't believe the idea that cat's will be pushed away from breaking waves if lying ahull better if they don't have keels, on the theory that there is no way a cat can accelerate fast enough sideways for that to
work.
Shuttleworth is an advocate of the "knocked sideways" theory of lying ahull if the cat doesn't have keels.
Dagger boards are sometimes canted against the
hull to get the housings out of the way of the
interior. Also, they don't have to be on the centerline, though it must surely be best to keep the exit underwater. I'd keep them off of the centerline, actually, to keep the slot from getting loaded with debris when drying out.