It's definitely not plain, but it has become boring through overuse. I love it, actually, but would never ever use it because it's been done to death.
Using
Lex as a nickname rather than
Alex does give it some freshness. I know someone who did that. Well, she named her son
James Alexander, because
James was the father's name, but she called him
Lex. Although the nickname gives it some freshness, I just don't like it. Makes me think of either a big dumb professional wrestler or an effeminate man.