I think the somewhat messy combo we have now is pretty solid. I mean, we've gotten bad results from it here in the States but some good ones too.
Pros: more common sense / practical result more of the time. Allows prevailing norms to play into law that is sometimes decades or centuries old. Permits flexibility in times of need.
Cons: less predictable. Allows prevailing norms to effect fundamental and important law (see, e.g., fascist Germany, modern-day Venezuela). Permits flexibility in times of duress/crisis.