Thanks for your replies. To answer your questions above, the ride is fully supported, so I won't be riding with heavy panniers, etc. I cannot take a second set of wheels as back-up, however extra spokes and nipples will be no problem. My current wheels (Easton aka Velomax Ascent II's) have several thousand miles on them and, I hear, are a bit prone to problems, but so far I haven't had any.
From your replies above, it seems like maybe custom wheels...Open Pro or DT Swiss rims with Shimano or Chris King hubs, with moderate spoke counts might be the best.
Also, would you recommend alloy or brass nipples?? Thanks, again