I see quite a bit more stuff among the regular middle classes that looks like pure signaling waste...

To take another angle on this, assume for simplicity that anything not wasted is "reinvested" in signaling. E.g. a Prius is somewhat practical and not just a signal, so more is spent on lawn care than if an SUV was purchased.

An important factor will then be willingness to borrow and be in debt, and Orthodox societies have a very, very high tolerance for this. One explanation would be the prominence of the LORD as provider.

There is one major signaling factor that the middle class does "spend" far more on, and that is aversion to certain government benefits (but not others, such as mortgage based tax benefits).