In the Steve Barton clip, ghostball is described and taught very well, especially the parts about guessing or estimating the aim line. After enough misses and makes, a player can certainly become proficient with it. It usually takes a while...the good ol rote or hamb method.
I'm not sure if a million balls is needed, but at least a few thousand might be required before you are able to consistently make more shots than you miss. And when you finally reach that point, that's when good aiming habits begin to develop, because you're able to successfully repeat more shots. Everything up to that point -- all the trial and error, the intermittent misses and makes required to slowly learn and fine tune your stroke and aiming guesswork -- was certainly time well spent. The results prove it. But I believe the same end results (a consistent stroke and good aiming skills) could be accomplished much quicker if the guesswork could be reduced or eliminated.
It's like this... I can show anyone how to draw Donald Duck, or a car or a bicycle or whatever, and after enough bad attempts you'll start to get an eye or a feel for how to do it. It might take a few hundred tries before you get really good at it, unless you just happen to have some artistic skill already. Now imagine this... Instead of just showing or describing how to do it, and you learning through trial and error, I give you a drawing and have you trace it several times. Tracing the known lines eliminates the guesswork and immediately gives your brain all the information it needs to start connecting those synaptic pathways that will allow you to draw the object free-handed, without thr need to trace it.
Does anyone believe the trial and error method would be quicker than the tracing method, as far as developing the ability to simply grab a pecil and paper and draw the object from scratch?
Aiming can be taught the same way, and a simple ghostball training template is proof of that. It eliminates or greatly reduces the guesswork. But it can't be used in real game situations, and during practice you have to set up every shot with that little device and work with it. It's still better than estimating or guessing where the ghostball is, and it allows for a much quicker learning method than trial and error alone.