What would demonstrate that it's worth it to you? Aren't their reused rockets significantly cheaper than the competition already? Or is there some catch here?
Are they? Have they re-used their rockets commercially, outside of testing? I was unaware of that, but I don't follow it very closely.
Did they not ditch the idea of re-using the second stage, as it proved too expensive? If so, that demonstrates there's sometimes a gap between targets and reality.
SpaceX milestone of using a Falcon 9 four times: https://arstechnica.com/science/2019/11/spacex-returns-to-th...
I'm not in the industry so I could be missing something (e.g. it sounds like there's a lot of competition in the light-lift market, cubesats and that kind of thing). But it seems that on heavy lift, SpaceX is dominating on price, and that seems to be largely down to reusability.
This would be an iterative process. First, figure out how to successfully recoup the rocket. Second, see what issues exist with the integrity of these rockets, and work to fix those. Try reusing. Find more issues, fix those, etc. Eventually/hopefully, profit?
https://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_... https://en.wikipedia.org/wiki/List_of_Falcon_9_first-stage_b...
I'm not sure what you mean by "illogical"; the idea of landing rockets has been around for 50 years. The issue is the technical challenges, and the cost. SpaceX have demonstrated that they have solved many of the technical issues, but haven't demonstrated that it's actually worth reusing rockets.
I suspect the same thing is true of digging tunnels. We have the technical ability to do it, but it isn't economically viable.