Randall Parker and most other people make several mistaken assumptions when they analyze interstellar travel. They implicitly assume that humanity is sending a manned mission with very little changes to our society except that there is the added capability of interstellar space travel sublight or faster than light.
I think that the economy of a country or world that is sending a manned interstellar mission will be 25-200 times or more larger than our current economy. This also means a world with 10-100 times or more greater energy production.
I think that it is clear that societies will spend first on developing the local solar system. So interstellar would be about 0.01 to 0.1% of GDP as most of the space effort would be in the solar system. The local space development should include space telescopes that will enable direct imaging of exoplanets. Some of the developments should also include multiple observation systems at the gravitational lensing point (500 times farther from the Sun than the earth). There should also be some development of the outer solar system, perhaps out to the Kuiper belt or Oort comet cloud. This can mean outposts going out half a light year.
It would also be foolish to send manned missions before sending robotic missions. Some of the robotic missions can send systems for scouting, preparing and developing the landing site.
I agree that a manned mission seems unlikely without major breakthroughs like Mach Effect propulsion before 2050. However, I am expecting major technological advances to prior.
There will be molecular nanotechnology 2025-2045.
There will be nuclear fusion for space propulsion. Early forms 2015-2025 and more mature 2025-2040.
There will be nuclear fusion for energy generation 2015-2040.
There will be successful cryonics to suspend and reanimate by 2045. If you have full blown molecular nanotechnology then you will have the nanomedicine for massive life extension and for starting and stopping cryonics or other suspension.
So I do not see the first manned mission as being some kind of half ass bootstrap where we are barely able to go (like the lunar missions). It will at least be like the early days of the colonization of the Americas where many ships easily moved about the Mediterranean Sea. We will easily be moving around the solar system.
There will be a base of technology. I also think that if you are going at 20% of lightspeed or less that you have accepted that someone else can go at 50% of light speed or faster when you are halfway and pass you. I would also think that any mission that would pass someone enroute would be very rude not to pick up anyone who is being passed.
Also, the first mission crew should still be hailed as pioneering explorers.