I find this excelent. The enforcement on higher abstractions is great. It might take longer to write the first time, but as we all know, its more important if it is easy to read then if it is easy to write.
To much clojure i see today has 20+ lines long functions with an abstractionlevel al over the map. Using midje will most likely help to even out the abstraction level and make it alot easier to read.