Having lots of modules that duplicate each other's functionality can be a problem in that new users have trouble finding the best ones and waste time, possibly also getting frustrated with CPAN and going sour on the whole idea of sharing code. Think about the torture awaiting a person who types "template" into the CPAN search engine.

Unfortunately, the metrics you talked about are not very comprehensive at this point. Maybe some day we will have enough votes for them to be more useful. Meanwhile, we have ad hoc attempts, like my article on templating systems. Several people have asked me to add other modules to this document, but in most cases I have to refuse, since the whole point of having this sort of document is to steer newbies toward the cream of the crop. Experienced people who have something specific in mind can handle examiing the suff on CPAN and deciding for themselves.

One thing that may help is the work that Leon Brocard did on CPANTS. He made some first steps toward automatic evaluation of modules based on some simple statistics. This could eventually be very helpful in fiding the best modules.