Discussion with a colleague today reminded me about a rubric that people sometimes use for assessing journals and reflective writing: Bigg's SOLO taxonomy. (SOLO=Structure of Observed Learning Outcomes) It is often brought up in discussions of deep and surface learning
It is described here and discussed in slightly more depth here and there are hints at applying it to essay-type work here.
If you think this is worth pursuing I will put these links in the sidebar and do some more research on SOLO and how it has been applied to reflective writing.