It depends, there are some very good comments/ideas on this FT china forum.

If your on the frugal side, then maybe not. If you can't speak chinese, then it may help to hire one for a few days. Some hotel concierge's are great, just do not use the 2nd shift ones at the cheap hotels. & expect the 5 star pre-planned hotel tours to be overpriced by double.

China is a money worship society, leverage that to get a good guide & if its a poor guide let the wife select another one the next day.