I agree completely with your analysis, BC. When I said one quinella equals two exactas,I was thinking more of the unit cost rather than the dividend. Irrespective of the odds of the chances of the first and second placegetters, the fact remains that you can cover both exacta combinations by doubling the cost of your bet.
I'm must admit surprise at the 12 month dividend result as I thought there was a definite bias, probably caused by the difference in pool sizes.
Good punting anyway.