My reasons for going with the rotary:

Less complexity (the typical pistons, valves, pushrod, etc. argument) which equates to Greater Reliability

Less Oil Burn : if you told me I was going to have to put a quart of oil in every 8-10 hours of operations for a car I would say you are crazy.

TBO - 50,000 miles is about 1000 hrs of operations. I have 90,000 on my Safari and it's going to go well beyond the 2000 hrs that I would get out of a Lycoming.

Back to cost - I'm not trying to save money by going with a rotary. I plan on top-notch parts, (i.e. ceramic seals, etc.) and having the engine balanced.

As far as Auto- Conversions, I'm not on board if it has pistons. 

Again, my motivation is the simplicity of a rotary, not cheap.