Advance results bring the Equus africanus asinus from Wikipedia first. Good. Basic results bring Donkey (Shrek) from Wikipedia second. Google might be onto something here .... but wait.... what is it there at number one for the basic reader... humm... "YouTube - Donkey Rapes Man". Hummm... who are our "basic" readers? ... gota think about this feature a little more.... ;) Meanwhile, a classic: http://www.youtube.com/watch?v=qRm8okHhapU
I would like it if Google expanded this to allow you to prioritize. Prioritizing advanced reading level documents seems like it would be of value to me.
It's worth nothing that, yes, effective communication means that the document should be readable by anyone, but it doesn't seem that Google is tagging pompous, impenetrable documents as "advanced". For example, the [donkey] search comes up with "All About DONKEYS!" [1] as an "advanced" text. It doesn't seem to be difficult to read, it is just information-rich.
The search for [cheese], however, doesn't sort the wheat from the chaff like [donkey]. Gnome's Cheese project, for example, is classified as "Basic reading level", and so is filtered out from the "advanced" search.