For both AMD and Intel, they continually tweak their processes once new technology is available. When AMD was at 180 nm, they were using tech that was developed for the 130 nm process, but could be ported to the current 180 nm process. They have done the same with their 130 nm process as well. So yes, AMD and Intel do improvements to their processes to increase the cost efficiency, as well as the performance. But they do not announce these changes as "we are moving to an advanced 110 nm process!"
Also, AMD barely has enough fab space to produce large quantities of their Athlon 64 and Athlon XP processors. Right now supplies are very tight for these chips across the world, and AMD cannot make enough of them. Why would AMD try to sell off some of their fab space to another 3rd party when they can't produce enough of their own chips? Dresden is running 24 hours a day, seven days a week. There is no room for a 3rd party design to be produced there, plus AMD probably would not want to take on the risk of doing foundry work.