"but it's much better for the economy that they spend it,"

Generally it isn't - because that tilts the economy towards producing goods and services that are wanted rather than those that are needed. Trickle down has been shown over the last 30 years to be largely a myth.

For example if you have public healthcare and private healthcare and there is a shortage of doctors then the wealthy "crowds out" the public healthcare system by purchasing private healthcare. Essentially they are using their wealth to jump the queue. Like the 'priority queue' at a theme park.