To be honest there was one I was courting in Iowa that wasn't much more than what I gave for my 16 row.  A lot of our fields tend to run on the small side so it's a lot of iron to drag around without much added benefit.  At least planting speed wise.

That being said, 12 rows are bringing more than 16 rows here.  12 row heads for the custom harvesters are all the rage.  I used to have a guy do my corn with an 8 row and now he refuses unless he can pick on 12!  WOW.. Business must be pretty good if the combiner can dictate to the farmer.  The next guy I got charges a full $5/acre more to run an 8 row than the previous guy with a 12.  Both run newer machines, both run deere chopping heads etc....