The pro is better handling. According to Todd Z, you want to use 1.25" spacers on stock rims. Just make sure you torque them to 91 0r 92 lbs., and use the "blue" lock tight that allows you to remove them easily.
Does it make that much of a difference, I don't think so.
As for cons of running wheel spacers. If you need to do brakes, you will need to remove double the number of lug nuts when removing rotors. Cheap spacers, like many found on ebay, are garbage. Many are not hub centric, therefore they can create vibration. Good spacers are hubcentric and will not cause vibration.
I'll have to agree with Tom. I have 1.5" on front and 2" on the rear strictly for the look. I can't really tell any noticable difference in the handling.
I do believe you get what you pay for with these....I'm not sure I would go cheaper.:unsure: