Yes the little +/- allows any resolution, to me it seems infinite.
Because Sonar is not a Wave editing program I would recommend using a dedicated wave editor for what you are doing, it will save you time and frustration. Try Wave Lab, Sound Forge or even Audacity.
In Wave lab the entire track is shown in a smaller view at the top. The larger edit screen is easily re-sized to and zoom in and out of.
You do need a certain level of zoom for working efficiently. There is a bar in the track view that shows you where the edit screen is zoomed to.