I've got some Kevlar housing on the tandem. I've only used it for brakes, with good results. It's not as flexible as regular cable, but it does not seem to compress as much either. Any brand of new cables, with a bit of TriFlow and proper adjustment, should provide smooth braking and shifting. The weight savings probably isn't much, but I happen to like the way it looks, and it was free.
I'd give Nokon aluminum housings or the Aztec version some consideration too. They are also low-compression.