I replaced my Stans with Light Bicycle carbon 29er rims (on some DT hubs I bought for the task) – what a world of difference. On a strict weight-for-weight comparison, the carbon rims are noticeably stiffer, something I didn’t think I would notice but did. I’ve ridden the last month minus a couple of spokes in the rear, as haven’t had a chance to repair, and wheel is still fairly true.
Hubs don’t make much real world difference except for maintenance costs and schedules – but if we wanted easy and cheap to maintain we’d all be on Shimano hubs.
My recommendation – go with Light Bicycle or similar carbon rims, and spend what you can afford on a good wheelbuilder. Have him/her recommend the hubs, and then try to actually take their advice (I’ve never taken Al’s at Wheelcraft, giving him ample opportunities for “I told you so” the next time I’m in).