Many of the streaked hostas are unstable and will revert to a solid or Variagated color. Often a new increase will be solid and you will have to dig and separate or the more vigorous solid color will take over and the streaked will disappear. Having said this some are beautiful and some people think they are worth the effort. Some are more stable than others and you have to study a little to determine which. To get variagated seedlings the pod parent must be streaked so many are used as breeders. I hope that made sense. I also meant to mention he best ones are often very expensive.
