We have a neighbor that has 30" equipment and it works well. They harvest it high moisture to pack into their silage pit. He likes 30 inch for lower equipment costs. Also, at the populations they plant (20 to 24 thousand I think), narrower rows really doesn't help. I think they are at about 14 inches between plants (probably can figure out the actual plant population from that number). At lower populations, a narrower row spacing makes the plants further apart in the rows but closer together row to row. It makes more sense to stay wider and have less row units per width of planter (i.e. a 12R30 vs 18R20 -both 30 ft, but 6 less units to wear out), and less units on the corn head.
Increase in Marketing > Increase in Yield > Increase in Land Base
Diverse crop rotation, increased residue retention and minimized tillage will increase yield and crop health more than anything we can spray or spread at litres or pounds per acre.