The weight of the OR compression sack is only 3.8 oz. Compared to the clothes inside this is a drop in the bucket. For winter I don't need a fully waterproof bag and would prefer something which breathes a bit. The summer might be a different story.

The air valve idea is interesting but the problem is that if the bag gets damaged, you have no compression at all.

It's true ironraven that it's a bummer to have to take everything out. In winter 'exposed to the elements' means snow and cold...not too worried about that. I could lay out all the clothes on the snow and repack them and they'd take on a minimum of moisture. If I did have to change clothes in the middle of nowhere I'd likely use my shell as a ground sheet since I'd have to take that off anyhow.