Light is always nice, but not at the cost of breakages along the road. (unless if you're competing, when a lighter wheel might be the difference between a podium finish or not. If you feel that a DNF is same, same as finishing in the pack, this might be an option)
Earlier posters make good points about traditional builds and the importance of tire pressure.
The precise number of spokes needed is hard to determine. Between build quality and riding style there's a huge space for varying experiences.
(ignoring differences in build quality) A cautious but heavy cyclist, good at going light and staying on nice surfaces can get away with a lot of things which would leave a lighter cyclist with a harsher ride stranded along the roadside.
But the main thing is that as long as you stay away from spontaneously taco-ing wheels and clearance issues everything else (with the possible exception of disc wheels) will still be rideable. The performance curve is a smooth hump rather than a sharp peak, so whatever you get will still be useable.