As has been mentioned, guys like Ziggler, Wyatt, Ryback and Miz are examples of wrestlers that started out with lousy and/or too one dimensional gimmicks but vastly improved their lot with some alternations, sometimes minor to sometimes major, to their personas.
Another example, from my perspective at least, would be The Undertaker. For the first year to year and a half, Taker's character was pretty dull and one dimensional. Most of his matches ultimately had him doing little to no selling with an offense comprised mainly of punches and variations of choking someone out. His promos were generally him saying a small handful of words after Paul Bearer had finished with his portion. While they ultimately kept the dark, macabre aspects of the character at the heart of things, Taker's persona gradually evolved over time into something a less hokey.
Another guy I think that deserves a mention is Triple H himself as he's most certainly come a long, long way from the days in which he was "The Connecticut Blueblood" Hunter Hearst Helmsley. Even though I personally liked the character, I knew that it wouldn't really sustain him as a major star and I liked how it changed slowly over the course of a couple of years.
