I have played for 50 years, and I rate things in Pool by efficiency rates and percentages. FWIW, I rate that a good Break cue will improve your Break by about 15%. Now, if that 15% improvement means that you make a ball where you didn't before, and gives you pretty good position, then the Break cue is entirely worth it. It is nice to make 3 or 4 balls on the break, but really all you need is 1 ball to go in, and halfway decent shape on the next ball to be shot. So, the bottom line is consistency on the break.
Redoing your break and form can also improve your break. Hitting the first ball solid is surely a plus, I have seen guys smack the head ball with no english or just low, balls scattering all over the place, and not one of them drops in. Every good player knows that if they hit the head ball a lttle on the right or left with a certain english, that they have a greater chance on making a ball on the break. In other words, some english will have a tendency to throw balls towards pockets, and some will throw balls out of the pockets, depending on where the cue ball is when you hit it, where on the head ball you hit it, and the english you use. A good example is the 10 ball break. SVB had the jump on most players in 10 ball breaking, but other pros have now caught up. I notice about 3 different places where they put the cue ball, and about the same english when they break.
Another example might be the 9 ball break to make a wing ball on the break. And yet another would be the soft break to make the 1 in the side that Alcano used to win a world championship.
Really, I think the wear and tear a Break cue saves on your playing cue makes a Break cue worth it. And most break shafts are different from playing cue shafts. My J&J break shaft is much more stiffer (13.25 mm), and has no give whatsoever when I break with it.