There is a very easy way to implent a rough tuning potential indicator. Right now we see number per execution. E.g. buffer gets / execution. That gives us no idea on efficiency. What we need to get a rough idea of tuning potential is buffer gets / row or CPU / row, etc. This measure is referenced as a rule of thumb in tuning literature. ( No link given for compliance reasons).
Of course the number must be used with care (e.g. account for GROUP BY clause), but it does make a good practicaal indicator.