Ostentation is always vulgar but extravagance is not necessarily vulgar—not by any means.
Extravagance can become dishonest if carried beyond one’s income.
Nearly everything that is beautiful or valuable is an extravagance—for most of us.
Always to wear new gloves is an extravagant item for one with a small allowance—but scarcely vulgar!
A laundry bill can be extravagant, flowers in one’s city house, a piece of beautiful furniture, a good tapestry, each is an extravagance to an income that can not easily afford the expenditure.
To one sufficient to buy the tapestry, the flowers are not an extravagance at all.
To buy quantities of things that are not even used after they are bought is sheer wastefulness, and to buy everything that tempts you, whether you can afford to pay for it or not, is, if you can not afford it, verging on the actually dishonest.