Consider people, period. How many people put more work into their things than their lives? It's not that hard to believe.
That said, as a writer (Sorta), I do like a nice, in-depth background to a character. Some of mine have gotten quite insane.
I, uh, have one family figured out back to WWI, with only a few gaps. 
My players run the length and breadth of that continuum. And who does what level varies from one character to the next. I've got a writer who regularly figures out family trees to 6 or 7 generations in addition to every childhood experience that shaped her character. Except when she decides she's tired of putting in that level of effort and tosses together a character from a seventh-sanctum or chaotic shiny random generator.
Then I've got the guys who define a rough box that their character fits in, surrounded with plot hooks for me to use. Their characters then get the finer details that really bring them to life through their interactions with said plot hooks.
And I have the people who are there to have fun with friends, but aren't the most comfortable with admitting their creative streak. They'll put in a few details about their character, usually physical attributes or some character trait adopted from a novel / movie / TV show they like and focus on finding ways to support the party in-game without worrying about having their own plot-lines to develop.
Of course, regardless of the type of player / character, the STUFF they buy can tell an awful lot about both halves of that equation. Someone who stocks up on guns, the player wants combat (or thinks there's little else) and the character is likely to be a bit distrustful and gruff. So yeah, satisfy his blood lust with combat once in a while, but also put him in light, "low pressure", social situations where drawing a weapon would be a game-breaker. Get him to play his expected niche, but also draw that character out with other situations, to see what he does, how he reacts. I've found the overwhelming majority of players are receptive, as long as the entire game doesn't hinge on their character being phenomenal outside their expected roles.