Excessive spending is really very individual.
Some people go into debt with their excessive spending habits.
Some people are so into shopping, their life revolves only around that and everything else becomes trivial.
But we can’t judge excessive spending in general because what one considers a necessity s/o else can consider that a luxury.
The bottom line is that someone shouldn’t spend more than there means, be so into attaining more materialism that they forget about their spirituality, or make untzniusdige simchos or build untziunsdige houses.