Usage patterns
〈人〉の金遣いが荒いsomeone's spending habits are reckless/wasteful
He's a reckless spender and is always short on money.
〈人〉の金遣いが派手someone's spending is lavish/flashy
She spends money lavishly, buying only famous brands.
金遣いに気をつけるto be careful about one's spending habits
Lately I've been trying to be careful about how I spend money.