I think there's plenty of ways to signal you're a good provider or good in bed without throwing the entire viability of both into money pits of useless junk. It just takes more skull sweat to figure that out on a case-by-case basis.

Sure, but now you're just showcasing a different skill set that has high survival utility, namely cognitive ability.

My hypothesis is that complex cognitive activities are one way humans measure fitness as a mate. Conspicuous consumption implies, "Hey, not only was I able to acquire all of this shiny stuff, I have so much I can afford to use it on useless things."