Everyone has an opinion as to whether or not Kuyt is "good enough", but the real question should be "Is he good enough to do the job Rafa wants him to do?". The answer, in my opinion, has to be yes. Kuyt's goalscoring in Holland could have been the main reason Rafa bought him, but has anyone stopped to think that maybe he wasn't bought for his attacking qualities? Rafa has shown with Valencia, and now with the Reds, that his philosophy can be summed up as "We'll stop you scoring and maybe nick one ourselves." rather than "Doesn't matter how many goals you score, we'll always score more.".
To this end, surely Kuyt is almost the embodiment of this philosophy? His ability in the opponent's box is not good enough for him to be considered first or maybe even second choice striker, but his ability to support the striker (s) and track back to defend is as good as anything else I've seen in the Prem. And this is the crux of the issue. Do you replace Dirk with a flying winger who'll score maybe 15 goals a season with another 10 assists but give us fuck all defensively? Benitez has shown his colours by repeatedly picking Kuyt to play the role which he is currently performing so effectively.
So when people say "Kuyt's not good enough.", they should say what it is that he's not good enough for.