I was surprised how hard it was even to start the spin
ChickenHouse,
It's a long time since I've spun a 172, but I don't remember it being particularly difficult to spin. What technique did you use to enter the spin?
I don't have any experience with spinning a 150/152 so I can't comment on the differences from a 172. I did spin a Tomahawk a few times. Now that was interesting!
westhawk,
I agree with you about experience of spinning being very useful. I was once teaching soaring to a young guy who was a 'natural pilot'. He learned very quickly and developed good skills and a good sense of airmanship.
One day, I was just relaxing in the back seat, while he was thermalling quite nicely, with half-flap about 5 kts above stalling speed (which is normal for most gliders), when suddenly we flicked inverted and started a spin entry. I took over and recovered. In retrospect, he must have got a little bit too slow and possibly applied too much rudder.
The interesting thing about this experience which has stuck with me over the years, was that my student, who had not yet done any spin training, was completely mystified by what had happened. He basically froze.
So, certainly in the case of gliders, I think spin training should be mandatory - not just incipient spins but three turn spins.