I can imagine a world with 20x as many machines (due to self-replication) but struggle to imagine a world with machines that are 20x as productive (due to other technology improvements).

A world where I can simply book a fuel efficient car via my smart phone and don't have to worry about issues like car maintenance and parking spots would probably have fewer cars than our world where car ownership is the standard.

Today my smartphone means that I don't have to carry around a street map. It serves as a audio recording device. It serves as a photo camera. It serves as a radio. It saves as a clock. It serves as a kitchen timer. It serves as my alarm clock. It serves as a telephone. It serves as an answering machine. It serves as a gaming console.

20 years ago I might have to carry around 20 different machines to do what I can do know with my smart phone.

Being wealthy isn't about having more stuff but about having better stuff that does what you want it to do.