I think Carl A's approach is a good example of the "heart ruling the head" approach, which is perfectly legitimate for those of us who are obsessed with detailing as a hobby.
If you want to try to stick with a "head ruling the heart" approach, you should consider what kinds of problems you'll encounter, and how often you'll have to correct them. For your own cars, likely kept in good shape with regular loving attention, I think the speed and power of a rotary is probably overkill. But if you have a lot of cars to do, or will have customers who'll pay to have a badly beat-up finish brought up to concours quality, a rotary will pay for itself quickly.
Of course, no guy ever regrets having another power tool, whether or not what you have now is "good enough"!