Although it's been around for centuries, Bomba rice is almost unknown outside of Spain. Even inside Spain, Bomba is far from being a household word. Those who've heard of it aren't likely to use it often. You'll almost never find it in use in commercial kitchens.
Nearly everyone in Spain has switched to the now standard Balilla because Bomba is so hard to grow. Even under ideal conditions, its yields are far lower. The plants grow too tall, making them much more susceptible to wind and weather related damage. I'm sure its struggle to survive adds to Bomba's inherently high flavor.
But, oh, the flavor. You really can taste the difference. Why? Bomba can soak up very large quantities of liquid while remaining very firm grained during cooking. It could take up two to three times the level of liquid you'd use for standard Spanish rice. In case you don't have your calculator handy, that could be about as much as five to six parts liquid to dry rice. All other things being equal, Bomba rice will be two or three times more flavorful when it's finished cooking.
Bomba may be many times as expensive as other paella rices you'll find. But if you're looking to prepare an amazing paella, splurge and get the good stuff. If you do nothing but buy Bomba rice (and then bump the input of broth up to the appropriate level), you'll immediately improve the flavor of the finished dish.
Zingerman's Food Tours is visiting Spain in October 2014. Join us for a behind the scenes journey to traditional food makers like this.