Just used Nation's vocabulary profiler on a newspaper text [original text, results]. The profiler is supposed to show you how difficult the vocabulary in a text is. If you were writing one of those simplified vocabulary graded readers like Oxford Bookworms that only uses let's say 1000 words, you could use this software to keep on track and control difficulty. This particular version at The Compleat Lexical Tutor also color codes the text to help you.
Now I have a complicated printout to interpret, ouch! Most of the AWL words are not the sort of words I would define for my students, too easy. Maybe a domain specific list, e.g. for economics, should be used too. The profiler allows you to add vocab lists. Here are the words that weren't in the lists:
"baht baht baht baht baht baht baht baht bangkok cane chakramon chakramon chakramon csb csb csb embarrassing ex fertiliser freight frustration hike hike hoarding inflation kilogramme kilogramme longstanding pesticides phasukvanich plaguing policymaking provinces quit reportedly retail retail shortages skyrocketing smuggling tackle tackle wholesalers"
I've define the expressions "hike prices" and "hoard" for students recently. I'd define "tackle" too. Detecting common collocations would be a nice add-on feature.