[spoon]

Although it is cleaner looking and more convienient to use set amount of bonuses and penalties (ie, +20 / -10), the various traits are not balanced. For example, +10 in space combat is worth far more than anything you could put in repair. See PvK's Balance Mod for discussions on this.

However, if you wanted to keep it simpler than PvK's point system, you could probably group the traits in three categories, and give equivelent bonuses per Category. For example, here's how I'd group the traits (without putting too much thought into it):

Good: Space Combat, Maintenance, SY Rate
Fair: Production, Research, Happiness
Poor: Intel, Trade, GroundCombat, Repair

Then, if you assign a +10 to a Good trait, you should assign a -5 to one of the remaining Good traits.

This should give you sufficient variation to choose from, I would think, and you could still keep the culture types fairly balanced.