I'm assuming you are considering using your same 4 row wide head, hence you are looking at 8 row wide planters?  Certainly, excellent corn can be grown in 38 rows.  If you go to an 8 row 30 planter, then would you go with an 8 row head or a 4?

Lots of combines can fit down a 15 foot hole, 6 row 30, but not near as many can fit down a 10 foot hole, 4 row 30.  We went from 4 row wide to 6 row narrow 15 years ago when we traded planters for $6k, and had our 4 row header turned into a 6 row narrow head for $4k.  It just made for a few less passes with everything, and our combine handled the change easily.  

This year we switched to 8 row, so we could plant a little faster, and spray faster ( we went from a 45 foot sprayer to a 60) and still spray 3 planter passes per sprayer pass.   We have 90 to 120 foot strips that are contoured, so straddling planter passes with the sprayer is not something we were going to do.  We were not going to buy a rigid 8 row planter, and try to drive down our country roads with a  25 foot wide planter, so we purchased a slightly used folding planter, and that forced us to switch to liquid starter.  We are in the north, where we need to put down starter, and that limited our options, maybe you don't use starter where your are at.  

I will say that going from 76 inch tractor spacing to 60, makes a tractor tippy and bouncy.  This year, we will be planting and spraying with duals for the first time ever.  Our planter and sprayer have longer tongues so we can turn without worry, and I am really looking forward to driving a much more stable tractor.  Good luck with your decisions