I do not agree with you. I like Mary very much, she is very classy, but generally speaking, what royals spend is not strictly speaking THEIR problem, because they get allowance from the State.
When Nicky Hilton celabrates Nrew Year wih a bottle of Champaign worthing 100'000.-- $, (source hello) it's really HER problem because she is not a public figur.
But all royals live from their respective States, and it's a big discussion held in many cercles about royals REAL use, so they have to be carefull not to provoke and to shock.
When a single mother working to a Super Market tries to raise up her child alone with a very low revenu, she may be disgusted by seing a CP wearing every day a different Louboutin pair of shoes worthing what exactly she earns per month, because this money comes from HER taxes also, so royals have to be carefull. You are right also for politicians, but the price of a politician's tie or his car are less evidenced than any CP's new crocodile bag. And they could be many people saying that a politician has an exact usefull role, and royals NONE!