A while ago I found and interesting round-table discussion from Ariba Live 2014 US on the topic of how to use amendments: http://www.slideshare.net/Ariba/amending-contracts-in-ariba-a-best-practices-approach?qid=4366af1b-48ee-4465-806f-2a660b5c3dd7&v=qf1&b=&from_search=1
I can to some degree see the logic of seperately registering amendments a workspaces, but I personally believe in the approach that Ken is also using - which is the way the system is designed to be working.
Ken, I would be very interested in hearing how you expect to be able to report on amendments, since this is a topic that I have also looked at previously, but without success.