I take your point about aileron/rudder but this is covered to a degree in effects of contols and turning? I found that covering slow flight at altitude without ground cues a little futile
As I think I said the other day, I'm just finding out about teaching this stuff. I do find that the true slow flight, i.e. a couple of knots above the stall gives a MUCH better demonstration of the effects of controls than you achieve at 80kt, which is the standard speed for Ex 4 in a PA28 (at our place, at least) Get it down to true S&L at 50kt, then get them to do a 15 deg co-ordinated turn, the stall-warner just coming on, I think is a really good exercise and also a good introduction to the attitudes to be expected in the next lesson, intro to stalling. I get them to fly at 50kt in all 4 flap settings. As Portsharbourflyer says, it also teaches the refined flying control required on final.
Also, many students approach the thought of hte stallign exercise with trepidation. This exercise allows them to approach it in a systematic way, so that tere is no drama. Mind you, in a PA28, it's all pretty benign, anyway.
Cheers,
TheOddOne