Ron,
The yield for corn in 2009 was 134 bushels per acre in NY, 111 bpa in SC, and 180 bpa in Iowa, so it's probably more expensive to buy, but more profitable to use, in Iowa.
'Too many' depends on location and population. Quite a few years ago I read an article on Myrtle Beach that said the area drew 4 mil. golfers per year (I forget the total number of rounds) and the existing courses were thriving. Somethng like 20 or 25 more courses were built after that, but the area never broke the 4mil. golfer threshold. I'm sure there were many owners/operators who thought there were too many courses in Myrtle.