I think his reply actually does address this, claiming that maximizing the interesting things you can do intellectually is best achieved by making a lot of money in a simple and not time-consuming or stressful way, and using the rest of your time to do those other things.

I think this claim might even be valid for some people, but for me (and possibly you) it isn't. See my other post. If neither of those considerations apply, then part-time service labor might actually be the best way to work on things that interest you intellectually.