I think most conservatives who listen to Rush do so just to reinforce what they already believe. The problem is that Rush, probably for commercial reasons, "compresses" 15 minutes worth of information into three hours of entertainment.
It's schtick.
Rush restates the obvious. Most know, and you are right when you say he preaches to the choir, what he is oging to say or where he stands. But it brings the faithful together. We listen and we beleive the same thing. He states it in an elegant fashion. He prioritized. This the left can never do. He can do it and still be enetertaining so that people cant wait until the next broadcast. Most who 'listen' to air america, (where it is playing), go through the motions of listening. In other words it is on as a show of support for their cause, but they dont listen or beleive.
Else, the gap between you and reason widens.