I saw a bottle of kefir at the health food store, and from memory there is about 8 grams sugar in it per serving.

Would the benefits of the good bacteria in the kefir outweigh the sugar content? Or should I give it a miss?

If you let the kefir sit for a few weeks or more in the refrigerator most of the sugar will be fermented.  Letting the kefir warm up a little to room temperature for a few hours will speed up the fermentation.  The sugars are destroyed in the fermentation process and more beneficial acids are produced.