Monroe does nothing to improve the Jazz. In a total dream scenario, it's a lateral move. Monroe's ceiling is a really nice complementary player with a noticeable lack of passion for the game and defense that will leave much to be desired, he'll never replace Boozer and he'll never amount to anything more than the team-mates that surround him. If the Jazz draft Monroe somehow and let Boozer walk, you can be excited for sneaking into the playoffs and Deron peacing out in a couple of years.
Cousins might suck, but he at least brings a damn ceiling to a team that rarely ever has one. However, if there's a chance for him to succeed, it's probably on a team with a coach that can match his temperament, a winning and stable tradition, a cast of high-character guys, a system that will get him looks, and the best PG in the game.