We have generally accepted metrics we use to measure how the economy is doing. Things like GDP, productivity, or even more proxy-like things like life expectancy and happiness.

Sure, maybe this type of activity counts towards the GDP in the short term, but long term a giant yacht isn't capital that is going to give a return on the investment. For other metrics it is useless as well. It makes 1 person (and maybe his friends) a bit happier for an extreme cost. I think by most metrics this is a poor allocation of resources in the medium or long term. It's just an ultra rich guy spending a ton of capital to make himself happy.