I've seen with building my team that salary is not that important. It's the skills of the player and how they fit with your team and tactics. Make sure your players have the right skills for the tactics you want to run and you should be successful. I want to have the best possible roster while limiting salaries. Getting a big salary player doesn't mean success if they don't fit your team.
Salaries are not important in the sense that adding salary doesn't necessarily provide an equivalent upgrade to the team. It is important in the sense that getting players with too high salaries can stunt the overall team growth.