Yeah, the trade-off is that you can go to much higher tension with paired spoking because the spokes don't have as much leverage to make the rim zig-zag along, since they're so close together. The theory then is that you can add tension and thus need fewer spokes. The problem is that between the spoke pairs, you have a large arc that needs to be structurally sound on its own (e.g. heavier).

So, you can have fewer spokes and a heavier rim, so the same weight. The aero advantage of fewer spokes is lost because there is greater turbulence between close pairs as they whip across the top.

Now you've got a wheel that at best performs as well as an evenly spoked wheel with four more spokes. But it's at higher tension, which brings it's own maintenance costs. Plus, if you break one of those spokes, you are more likely to crash from it since it will throw the rim further out of true.