Contrary to popular belief vertical stripes do not make you look taller.Anyone taking more than a cursory glance will realize that the person with the vertical stripes is as short as they actually are.Designers and old wives will continue to try to fool people with the vertical stripes myth that has been around for ages.
It depends on your body type. I think if you are thin and moderately considered shorter they will add more inches. If you are taller and thin they will add less inches. If you are chubby and short they will not help, at all. If you are chubby and tall, you will get a couple inches , but not as many as a thinner person. :) Hope this information helps steer your fashion/style choices in the right direction:)