I'm reminded of the _Nicomachean Ethics_, which, if I recall accurately, begins with an analysis of what you're calling instrumental activities vs terminal, in order to show that the end goal of any activity is happiness, which is not instrumental for any other purpose.
I'm not trying to go too deep into philosophy with this concept. I guess one could present a convincing argument that there are no real terminal goals, or that the real terminal goal is happiness, or something like that.
From the practical perspective though, people seem to have a limited capability for introspection. Maybe for Musk solving the big problems/retiring on Mars is only instrumental to feeling righteous, which is only instrumental to being happy, etc. but humans don't usually introspect that deep. The recursion stops somewhere around the moment where you feel you care about something for the sake of that something. That's what I meant by terminal goals here.
