Mixed feelings for me. After a century, the local ecosystem has long since adapted to the rainbows' presence, just as it had to the wolves' absence. There is a big ideological war going in in park management, looks like the 'make it all just the way it used to be' faction is winning.
But... is it right to assert that a national park has solely environmental value and not economic? Although it kills some park managers to admit it, parks are there for people too. Like it or not, economic activity develops around them to greater or lesser degrees. Just like the aquatic ecosystem that adapted to accept the rainbow trout, the guides and tackle shops have slowly become part of the economic system anchored on the park. In both cases, arbitrary choices based on ideological principles will have some unpleasant side affects, not all of them foreseen.