I have operated and instructed in a large variety of aircraft types and assure you the majority require the master switch to be on for them to operate (the pre-flight inspection soon determines that). I hope my "blanket statement" concerning stall warning devices result in readers determining the situation in the various aircraft types they operate. I have a couple of hundred hours in a Beech D18S, the type could safely operate without any stall warning device as the pre-stall buffet is quite pronounced.
Stall recovery training is no where near as important as learning the symptoms leading up to a stall, so recovery can be initiated before the stall. These symptoms/cues vary between aircraft types and include placement of the flight controls as they control angle of attack and slip/skid. To say aerobatics are of lesser value than the spin recovery training is an ill-informed take on aerobatics. You spend a significant portion of time at/near/beyond the critical angle in a number of manoeuvres. Spin recovery training is of little use to a pilot who unintentionally enters a spin at or below circuit height. A pilot who allows an aircraft to enter a spin in the circuit is unlikely to have the skills to recover before hitting the ground. Again, learning to recognise an impending spin and initiating recovery before it develops is far more important than spin recovery.
I'm not saying stall warning devices are a bad thing, they are way down the list when it comes to avoiding an unintentional stall. If you consider the stall training delivered during abinitio training is adequate, you really should find a good instructor (current aerobatic pilot) to do further training in the types you operate and with the C of G in the range you would normally operate at.
I appologise for ranting, but the stall / spin accident rate would reduce significantly if pilots received proper training.