jags, my bike was an ex-display bike, so I assume SJSC built the wheels. The wheels overall are good, I have had no problems with them at all and they are still running true. I am not an expert on rims, I am quite a newcomer to 26" wheels and for 700c I always got the best Mavic's I could afford, so I am not an expert in rims for your Sherpa. However here goes with the little I do know and what I can glean from Andy Blance's advice.
The Rigida Grizzly CSS rims are reportedly lighter than the Andra, yet they are strong enough for a Sherpa, so therefore a good compromise somewhere between an expedition wheel and a lightweight touring wheel.
Sherpa option description "Grizzly 36h Other people’s heavy duty rim; this is our medium duty rim. Ideal for road based trips. Lighter and quicker than Andra but not as “bombproof” or long lasting.".
I think they are light enough for my RST, but not that far away from the rims on your Sherpa to warrant such a significant investment in cash terms. Braking in the wet with CSS coating isn't nearly as good in the dry with blue Swisstop pads, some get on better with alternatives.
If you want a lighter/faster rim Thorn recommend the DT Swiss XR 425 rims.
Andy Blance's comments in the current Sherpa brochure:-
"Rigida Grizzly rims
These are our preferred choice for most Sherpa bike builds. They are reasonably light in weight but they’re certainly not ultra lightweight rims,"
"DT Swiss XR 425 Rims.
These are cross country racing rims. They are very lightweight and can certainly encourage you to make big efforts...they are seriously quick. They are only suitable for lighter weight cyclists on lightweight tours."
If you like Rigida rims there are also the Snyper which is a general purpose rim and is much cheaper than either of the above, mostly used for cummuters I think.
Mavic rims offer a good range of MTB racing rims which I would imagine would give you light weight and speed, a brief outline of Mavic naming conventions is:-
the letters
XC = cross country
XM = cross mountain
EX = extreme MTB
A = asphalt (road)
First number is rank in Mavic heirarchy e.g. 7 > 2.
Next 2 numbers = internal width (e.g. 717 is 17mm wide, 721 is 21mm wide).
Therefore a Mavic XC717 is a cross country rim (faster than XM or EX which I take to be more impact proof), 7 series being high up the range, and 17mm wide. This should be one for your shortlist along with the DT Swiss above, I would count out the Grizzly as being too much of a heavy(?) touring rim.
The Schmidt SON dynamo hub is excellent, very little rolling resistance - so low I am not aware of it. One thing to consider, I have an allen key skewer in mine and to begin with I struggled to get the right torque on it - very small margin between being too loose and too tight (causing a notchy sort of rolling resistance) - but that doesn't seem to be such an issue for me now, maybe I got used to it. I am more used to quick release skewers, but with such a hub you might want to consider the Pitlock skewer.
I hope this gives you a starting point jags, but there will be a few contributors on here who could give you much better/fuller advice.
Good luck with your wheels jags