Whether to pack spare cables doesn't matter from a weight standpoint, but the question is important in the larger context of how much in the way of spare parts and tools you should carry.

I've only toured in the US and a bit in Europe. The only spares I carry are two tubes, a patch kit, a fiber flex spoke, a spare chain link, and some duct tape. I have a multi-tool and a leather man and that's it. If I was going to Mongolia I might carry more, but as long as I can make the wheels go around I figure I'm ok.

Get the bike checked out and new cables installed before you set out and you will be ok