I agree that they don't exactly make pretty engines, but the fact that they stuck with the rotary valve, and therefore reigned as the undisputed kings of horsepower, really earns them points in my book. I'm a very big fan of rotary valve induction, especially after hearing reports of a 250 Green Streak (which is so heavy you can barely get it in the truck) riding a 10-years-newer, comparatively feather-weight 250 Husky. The big, heavy rotary-valve bike positively walked all over the reed-valve bike, regardless the big differences in weight, suspension, and frame. That particular Husky did have some problems with it, so now we estimate it's either as fast or maybe slightly faster than the 'Streak in a straight line. Like Gordon Jennings said in his fabled handbook, "in the world of karting, where there is much more experience with both reeds and rotary-valves than motorcyclists have accumulated, the two types of engines have been separated into different classes. Why? Because while the reed-valve engines are inexpensive, they cannot match the performance of those with rotary-valves."
That book was written in '73, so I don't know how relevant it is in today's world of case-reed engines. I imagine the simple factor of cost and ergonomics (rotary valves generally lead to wider cases) have been the deciding factors in axing rotaries lately. But if I were determined to get a maximum of power from a minimum of displacement, width be damned, I'd use a rotary valve (and a supercharger!)