Assuming the price and availability of the hubs is the same, I don't think there would be much of an advantage running 28 with that setup. You are sacrificing durability for weight savings on a wheel with hubs and rims that are pretty heavy by themselves. I think the weight/aero advantage of a low spoke build is really only worth it in a 'race only' wheel situation.
I'd say the same with the bearings. The seals in a low friction bearing are worse at keeping out the elements, sand, grit, etc, and really only provide benefit in race situations that only occur in good weather, i.e. the track. The amount of extra drag a well sealed bearing is nothing compaired to the rolling resistance added by patches of gravel and mud.