Any real advantage with spacers?
 

Or just looks?

Mine has 5mm spacers. What would 10-15mm spacers do?

205/50.
255/40.

Spacers are the equivalent to botox when it comes to wheel fitment augmentation. When done right and in moderation they can transform the look and feel of your vehicle.

You can use spacers to optimize performance with front to rear track, or you can just be a poser it trying to achieve a certain look - it's your call.

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.

On my S, I put 15s up front and 23s out back....and yes I have too much under steer. This together with old suspension compenents are a problem.....I can feel my outside front "folding under" on medium speed sweepers especially when there is a disruption in the road surface.

I was considering going to 20s on the front but this may qive too much feed back and feel through the wheel. The steering effort is already fairly high..

Don't want to pull in the rear spacing as I like the wide stance look for the street (posing on the street:))