[thstone]

Increasing the track width at both front and rear equally will have some minor handling benefits like slightly quicker initial turn-in feel while maintaining the stock handling balance (tending towards understeer). I won't address the visual aspects of spacers.

As LAP1DOUG suggests, the biggest bang for the spacer buck comes from optimizing the front to rear difference (e.g., 15mm in front and 10mm in rear for a difference of 5mm - please note: this is an example only, not a recommendation!). This will give two potential improvements: (1) the 15mm wider front track yeilds quicker initial turn-in feel; (2) the 5mm increase of the front track over the rear track will tend to reduce the amount of front understeer (increase oversteer).

Doing this "optimally" will bring the car to a more neutral handling balance (equalizing understeer and oversteer). But be careful, this approach makes its easy to create an oversteering beast.

Generally speaking, most people who are willing to work this hard to get a neutral handling car already have adjustable sway bars which makes the adjustments simpler and easier than messing around with different spacers front and rear.