Personally I think speed is generally overrated for the reasons you mention, if you type at around 100WPM you probably won't be significantly limited by your fingers for any practical task. For me it's more about comfort, I switched to a better keyboard and the Dvorak layout because I started to have wrist pain. I don't know if dvorak is all that superior to qwerty but it gave me an opportunity to completely re-learn how to type since very few keys line up, and this time I tried to learn proper hand and finger placement etc...