There is no way you can compare the replacement of Three Rivers Stadium to replacing Wrigley Field!
Three Rivers/Fulton County/Riverfront/Busch stadiums were all cookie-cutter stadiums that were barely tolerated, much less loved by the fans. (I still lament the loss of Crosley field to that concrete behemoth known as Riverfront) This is why when Pitssburgh, Atlanta, Cincinnati and St. Louis all demolished (or completely refurbished to make into a ball park) these cookie cutters few cared and some cheered! Though I like Great American Ball Park, it is still not a real "old" ball park and I have no real connection to the place.
But when you contemplate tearing down historic fields like Fenway or Wrigley fans will protest! They are old, run-down but they are a part of the fans' living souls! I am not a Cubs fan. But I go to at least a couple of games at Wrigley (even when the Reds aren't playing there) just because it's wrigley field. And I am still ANGRY they added light to the field! Really! There would be no reason for me to go to Chicago if that field is demolished in favor of a new stadium.
Baseball, unlike any other sport is deeply tied to nostalgia. There is an intrinsic value to being able to sit at a stadium where Babe Ruth played. Where some great history was made. Fans feel connected to the entire life of the game, not just the game they are watching that day. It's about the smells, the grit and the entire ambiance. No new park, no matter how "retro" can capture that.
I would hate to lose one of the last two remaining old ball parks for not other reason than to keep up with the Joneses.
You can gut the place and renovate. Get Bob Villa back with the This Old House crew and make some magic that way, but don't tear down a living piece of history because "it's old".