Things certainly do evolve, I'm just a proponent of the idea that in comics, regression isn't always a bad thing. Superboy is a good example, and since its also the topic is more apt: He "evolved" thanks to Johns into an angsty guy worried about turning evil like his "dad". Making him more of a carefree teen would technically be a regression because it'd be going back to the old way he was. But I feel his old portrayal was leaps and bounds better, so I'd take that regression in a heartbeat.
To use another example: Bart Allen. Yet again thanks to Johns (this is not a coincidence), he went from his own individual in the Flash mythos, the off-the-wall with energy Impulse, to a pre-Crisis Wally West wannabe in a new Kid Flash. In technical terms he evolved, he "upgraded". But the character became less interesting, less unique, less everything. Regression would be fantastic there too.