Genghis - you eloquently point out that there is no such thing as stalling speed for all practical purposes. Sure, a speed at which an aeroplane at a given loading (G and weight) will stall can be calculated if you have all the data, which you don't.
An AoA indicator gives an unequivocal direct simple read-out of how close to the stalling angle you are.
Agree with Mono that the next best thing to an AoA indicator is 'your arse', or more correctly the 'feel' of the aeroplane. If you are familiar with the type, and esepcially if you aerobat it, you will know how the controls feel just before it departs (this assumes you are creeping up to the stalling angle gradually, as one would be on approach; a sudden hard pitch up might put you beyond the stalling angle with no warning signs).