saying I had nearly put us into an inverted spin, which was not recoverable
Hmm... Maybe the instructor was commenting on a specific type with bad inverted characteristics...but inverted spins, flat spins and flat inverted spins and accelerated spins are generally ALL recoverable....
Check out a book called 'Spin Management & Recovery' by Michael C Love - an excellent book that covers ALL forms of spins...very very informative.
With regard to spinning down through cloud - you must be a idiot to do that. In the PA28 reduce the throttle to idle, select full flap, and trim aft FULLY to keep the nose up....and let go of the controls...suprisingly it enters a very mild and gentle spiral and leaves HUGE amount of time for recovery at the bottom at normal speeds in a sensible flight attitude....very enlightning when I was first shown this... (we were discussing descent thru cloud with NO instruments...i.e. ASI/ALT only...)