The dream of space exploration & colonization is that it's a stepping stone towards other worlds and a vast spread of humanity across the galaxy. Not simply a one-time deal that adds a new region of Earth for humans to live in, but at great expense & difficulty.
Earth to Mars (shortest): 56,000,000 km
Earth to nearest star after the Sun: 40,000,000,000,000 km
I think you need to make the same kind of leap as going from horse and carriage to the Saturn V to go from interplanetary to interstellar. Sure keeping people alive is an interesting challenge, but somehow I don't think generation ships that take ~70000 years is the solution. For that we need a revolution in propulsion technology that we're not going to get from Falcon Heavy, SLS or even Musk's ITS. A bit like if I wanted to lift 100kg, I could do that with exercise but none of those plans or experience really bring me closer to lifting 10000kg.