I also feel that grinding is overused in MMO's. We should encourage developers to look for more creative or interesting ways to provide longevity. In the meantime though, as long as the game provides something interesting to do, it's worth it to keep playing. If you don't know what to do for yourself, maybe consider assisting other people in achieving their goals. Help newer players progress or learn about the game, or something along those lines.

If you really feel like there is nothing to do, stepping away from the game for some time is fine too.