Hi emil9216,
A good question. I never tried a WYSIWYG XML editor.
When you load a Blogger XML template in Dreamweaver and look with Design View ... there is not much to see. Doesn't work, I guess. Or I am missing something.
But google
WYSIWYG XML editor and you will get plenty of hits. So yes, there
are WYSIWYG XML editors. (I didn't know that

)
Said again: a Blogger Template doesn't show much.
What I always do: design a new layout in normal XHTML ... and when finished ... 'translate' the code in(to) XML (including all specific Blogger code)! That last process is indeed done pure manually!
Regards.