Thanks for your help.
You could consider the WordTable plugin, which lets you create questions using Microsoft Word tables. You can export questions into Word, edit them, and import them back as new questions. In the background it uses Moodle XML, but you don't need to worry about it. You can also install a Word template to assist in creating new questions. These are separate from the plugin, and are available on a different website: www.moodle2word.net. It's not plain text, but quite easy to work with if you're familiar with Word.
I had a quick look at the LaTeX-based approach using moodle.sty, and it is amazing, but really only for the dedicated TeX enthusiast.