Wheel spacers are not a bad thing... But let me first address a few points: if you are buying a brand new set of wheels, do not get wheel spacers - your paying for a set of wheels supposedly designed fit your car, make sure they fit right. And as far as "ruining your car" goes, there should be changes in suspension geometry and chassis balance - both of which are improved with wheel spacers, particularly on stock wheels. But changes in suspension loads, wheel travel, braking performance, and my favorite "making your car do painful things it was not designed to do" should be non-existent with the right wheel spacers (you know, so long as the wheels don't stick out of the wheel wells like a low rider on wire mesh wheels...).
Wheel spacers, especially on stock wheels, help improve handling - and generally make the wheel look a lot better in the wheel well. The GS400 is a good example of a car that is improved dramatically with wheel spacers, in both looks and handling...
And if you're going to use a set of stock wheels to race (track events) - David, a set of wheel spacers should offer improved handling.