So I get the nastalgia thing. It's a fine venue with really cool staircases and a killer sculpture.
The symphony isn't much of a factor in the economics of downtown. Two pro sport franchises and an entertainment district are major economic contributors. While I hope they can leave Abravenel alone it may need to move or be relocated ont he block in order to make the new district work. There's no way that the Utah Symphony doesn't end up with a home.
The notion that a new facility can't be as good or better is nonsense. No building built in the seventies is irreplaceable.