Sean McGrath: The real beauty of messaging is the tremendous scope it provides for intervention in message flows. Where you can intervene, you can transform and Transformation is the only truth.
I agree. However, I would like to add that once you accept that, you can go on to produce better models, ones that are more suited to transformation.
For starters, it helps if the messages are cleanly and thoroughly specified. And adopt the use of a common set of data types when possible. And ones that don't obscure structure with XML escaping.