Time with team does seem to help. I've generally been 25% to 50% above league average with low to average overall salaries (and even now when I'm right at the league average salaries, I don't have a lot of big salary guys eating up huge minutes). I'm right around 43k per week now with a decent run this season.
I'm partially with w_alloy on this. The merchandise income itself is far less significant than making sure that the players you do have are salary efficient. But if you can manage to have a lot of homegrown or long-term national players who also fit that salary profile, it's the best of both worlds.