Lots of interesting stuff but some rather off the ball answers!
Send Clowns ... I'm sure your "keep the speed up" bit was simply to try and add a safety margin, but it's really misplaced over-cautiousness. It's actually very difficult to spin from a side or forward slip. Two main reasons, but don't take this a wholly true as there may well be exceptions! ... Most aircraft will tend to run out of rudder authority before you reach stall and will naturally start to turn back into trim. You will by then of course be VERY near stalling so it won't take much to tip the balence but you'd be a fool to miss the signs. Also, unlike skidding manouvers, you are in a pretty safe configuration as the inner wing (relative to airflow) has a better "bite" of the airflow unlike outer wing which would cause that wing to stall first. As the slightest easing of rudder pressure will swing the outer wing back into relative airflow faster than the inner wing it will very quickly take hold again. I'm probably not very good at explaining this, so go up to height and try it. I was taught to completely ignor ASI when slipping but this was basically because a glider has a pot pitot which is VERY inaccurate in the slip. The habit stuck though and I find it's easier to go by attitude and feel. To slip effectively though, you will tend to find you need a slightly higher nose up attitude than when you fly "in flow" to keep the same airspeed. It can seem a bit scary until you get used to it but there's no point in letting the nose drop in a slip because you will loose all that short landing advantage by the ensuing float.
I note of caution ... some homebuilds and I guess some factory types don't have the strongest of sternposts. Slipping is OK at slow speed, but not at all appropriate at too high a speed as stressing will be high!
C172 slipped very well. I was with an instructor at the time and he was under the impression that what he called a myth was to do with elevator blanking. I hadn't read the POH and I guess if I had I may have not been so enthusiastic. However, it slipped beautifully, came down very quickly, which in itself is dodgy as all that downward momentum takes some checking! To be honest with those very powerful barn door flaps, the one aeroplane you really don't need to slip IS a 172
SS