"you probabily have some of poor quality and some good."

It is not always clear whether a module had bad quality. Not all the people use the same standard, and even for the same people, he/she doesn't always use a consistant set of standards.

"Should the "bad" ones be stopped before they reach CPAN?"

They should be stopped, if we know which one is "bad", but do we know all the time? do we always agree with each other?

"Or shouldn't we take advantage of the newly added rating feature for CPAN modules to tell the good from the bad ones?"

Well look at the XP point system here.

However it is not hopeless, stay with this site long enough, you will notice that some modules being repeatedly positively mentioned, and probably you should give those a try.