I recognise that there are possible problems with the construction (See the criticism of Luz, Matthew 1-7, pg. 191 n. 59), but it does appear to make more sense than the usual interpretation, which ignores τῷ πνεύματι.
France, The Gospel of Matthew, pg. 165 sees this as a "poverty in spirit" but in a positive spiritual orientation, the converse of the arrognat self-confidence which not only rides roughshod over the interest of other people but more importantly causes a person to treat God as irrelevant. This is closer to my understanding, but again, it forces πνεύματι to refer to the human spirit which is impoverished or lacking, when Matthew's usage suggests a reference to the Divine Spirit.
Thoughts? Have I missed something?