Extravagance means needless excess; miserliness means withholding appropriate expenditure even where a genuine need or right calls for it. Moderation is the balanced path between the two.
Paying for necessary medical treatment differs from buying an unnecessarily expensive item merely to impress others. One responds to a need; the other increases spending for display.
The report values sound judgment in spending. نِصْفُ الْمَعِيشَةِ does not prescribe that exactly 50% of income must be assigned to one category, nor does it guarantee immunity from every financial difficulty.