A simple suggestion: expand a collapsed track by double-clicking on it. Intuitively, I expected this to work. It would be more convenient than pointing the mouse at the tiny arrow (maybe it’s just me, but I find it very easy to miss).
Also, in the mixer view, double-clicking on an ‘unclickable’ part of a track (like the level meter or an empty part of the effects area) could collapse a track. That way, you could very easily expand/collapse tracks in the mixer view. I can see myself using this a lot.