Old post, but I thought I'd respond. I think it is worth doing.
I got the following quote from another BMW forum:
The rebuild kit is just a new valve stem which just retains the TPMS sensor, there is nothing on the sensor itself that is rebuildable, the valve stem retains it and they are just replacing the valve stem itself nothing else. If it has been a bunch of years, probably worth doing a new valve stem, normal to do them with tire changes in the past as they are cheap. $5 a tire is worth doing just to make sure you don't have a leaky stem!
My father's GMC truck has stupid TPMS and Firestone requires these to be replaced. I assume BMW TPMS is no different - just the valves, o-rings. If this is so, then the replacement kit is nothing more than asking if you want your tire stems replaced every time you change your tires, which most people do do.