See this is the kind of thing that's not helpful.
It's just an outlandish overly optimistic mishmash of different concepts.
Let's start with your analogy:
> Imagine if a round-trip flight from the US to Europe didn’t cost $500, but only $5, unbelievable, right?
If you mean to use this to explain that what today costs X will in the future cost 0.01X, you're probably right.
But a more accurate analogy is "Imagine if a round-trip flight from the US to Europe didn't cost $50,000,000, but only $500,000, unbelievable, right?"
Same ratios, but deeply different implications.
Today, the idea of setting up a continuously settled Mars colony - hell even a Moon colony - is unfeasibly expensive. It's ACHIEVABLE - we have the technology and the money - but it would cost an intolerable percentage of the GDP of the world to accomplish.
A 100x reduction in costs means that it becomes a fundable endeavour that countries like the US could still justify.
We're still talking about generations - maybe a century - away from someone being able to just pop over to Mars for a summer vacation, the way that a college student could to do today with an intercontinental flight.
> Many things we see in sci-fi, like lunar and Martian cities or orbital cruise ships, could soon become reality.
For a very generous definition of soon and for a highly implausible definition of what a "cruise ship" is - it'll never be as accessible to the average person as earth cruise ships. Not as long as you keep using rockets.
Regardless of reusability, there are realities of fixed FOSSIL FUEL costs associated with getting into gravity. They're not cheap, and they're not frivolous. If you want to be able get things into orbit as cheap as you're suggesting, you need to start investing in a space elevator, which noone is right now.
> Personally, I can’t wait to see a massive, kilometer-wide telescope in space
Cool, yeah, that's true, that becomes more available.
> or nestled in a crater on the Moon.
..why?
> We might finally figure out dark matter, dark energy, anti-gravity.
And the final cherry on the cake. Humanity becoming inter-planetary is important on a macro scale. And trying to go further and further into space will INCENTIVISE research into these concepts.
But in no way does getting to orbit cheaper make it easier to figure out any of these concepts. There's nothing we can do from Mars or on the way to Mars in terms of this science that we can't do from Earth.