The whole notion of data vs. programs sucks. XML is based on that notion, sexprs aren't. This is why sexprs are superior.
I like the Lisp approach for now: its very convenient, flexible and above all simple. Learning Lisp is on my Someday/Maybe list and when I get around to doing that, I'm looking forward to revisiting this problem.
See also XmlIsaPoorCopyOfEssExpressions