Anecdotally, I've also used webMethods, SSIS, and several other visual dataflow programming languages, and they look remarkably similar to FMJ.
> Each single graphical element had 2 or 3 different XML "source" files, distributed in different subdirectories
S-expressions with equivalent content are smaller and just as readable, and don't need an extra parser. XML is OK for text mark-up, but not as good for storing data (including programs).
I would be more than happy to explore viable alternatives to traditional text-based development but so far I haven't found anything that really impressed me.