The diplomatic cables contain all sorts of information about extraordinary rendition, about the use Turkish airbases, Irish complicity, etc.
This isn't small potatoes. Here in Sweden it wasn't just the extradition from Bromma in 2001, but the US flew multiple illegal flights with prisoners through Sweden, possibly to the US torture camps in Poland and eastern Europe.
I also think these cables revealed information about the Thailand black site, where the US was torturing some people.