If you look at it carefully, we already have a Lance Stephenson-type player on the roster: Evan Turner. Let's take a look at the statistics this year:
Stephenson: 31 mpg, 9.8 points / 6.1 reb / 4.8 assists / .7 steals / 2.3 TOs
Turner: 25 mpg, 9.2 / 4.5 / 4.4 / .9 / 2.4
The raw stats are very close, but this is a case for normalizing things PER 36:
Stephenson: 11.4 / 7.1 / 5.6 / .8 / 2.7
Turner: 13.1 / 6.4 / 6.3 / 1.3 / 3.4
That's so close it's almost uncanny, especially for players who (nominally) play the same position. Even their personal "best" years of their career are similar when looking at PER 36 numbers: 14/7/5 for Lance and 16/6/4 for Evan.
Lance has better potential, is better at the defensive end and 2 years younger. But he's also a known cancer and carries a $9m/yr price tag for 3 years. Turner has fit in well with the Celtics and costs $3.3m this year and next. So when considering everything - the stats, the attitude, the contracts, their respective ages and that all elusive "potential" - would anyone really take Lance over Turner? I'd say Lance is the better player, but not by that big of a margin. When factoring in the attitude and contract, I'm happy to have Turner instead.