Steve
Mostly Harmless
Economy is an excellent example of one possible criteria for evaluating effectiveness. Absolutely.It's not just about how effective a technique is, but how economic it is. Let's compare for example a roundhouse kick with a tornado kick. Both kicks are relatively safe to perform and can do a lot of damage, but the tornado kick requires a lot more energy to pull off. In a fight you don't know how long you will be fighting for, and generally want to conserve your energy. After all, there's no point in doing a bunch of tornado kicks and exhausting yourself at the start of the fight.
But you also bring up another point. While a tornado kick is a very flashy kick, I know that there are many martial artists who would also consider the roundhouse kick to be flashy. I've heard said around here that anything above the waist is just showing off. And that's just a roundhouse. There's also a spinning roundhouse that's somewhere in the middle.