Wouldn't it be more practical to search for signs of extinct technological extraterrestrial civilizations?

How do you search for extinct civilizations? SETI is searching for radio or laser messages from aliens. That is easy to do because we can do it without ever leaving Earth. Of course an extinct civilization can no longer send signals. To detect an extinct civilization we have to go to their planet and dig there. So far we haven't been to any other planet, although we have landed some remote controlled robots on Mars. No evidence of any extinct civilization has been found on Mars.