Big difference---there were 4 regional semi-states. That added the geographic dimension which was the original driving force behind the NCAA, while retaining all great local rivalries leading up to the FF. It was the perfect mix.
Think about how entertaining your idea would be, or letting all 353 in, if we went back to the idea of a regionally based tourney. Maybe a final 16 that looked something like this:
East:
UNC
Duke
Georgetown
Pitt
Midwest:
Indiana
Purdue
Michigan
Notre Dame
South:
Kentucky
Florida
Texas
Oklahoma
West:
UCLA
Gonzaga
Arizona
BYU
or maybe Evansville, George Mason, or SFA or a few of 20 other teams knock off 6 or 7 of these teams....