@peragogo, I hear you about math. I like going with 2 positive and 1 negative trait myself, except I'm not always good about assigning the negative.
Going with 12 zodiac signs is tricky because you're never going to get them evenly divided, but you could throw in a few "cusp" days where you could draw from either sign for your traits and other characteristics.
Back when I was playing TS3, I assigned each trait to a zodiac sign and tried to use those when the Sim aged up. But it was always unsatisfactory, because the zodiac signs had no relation to the time of year.
Your Scorpio example looks interesting. Thanks for letting us know about your system!