As a tourist destination, perhaps. As a self sustaining colony absolutely not. Since you have to float in the atmosphere to survive, mass is at an enormous premium. On-world industry would be nearly impossible.
If your goal is to build an exotic resort for billionaires go to Venus. If you're trying to ensure the survival of humanity in the event of a planet-scale catastrophe go to Mars.
Going to Mars would contribute exactly nothing to the survival of humanity, because everybody on Mars would remain absolutely dependent upon frequent shipments from Earth.
Any attempted Mars colony would die out not long after the last shipment, as materials necessary to its continued survival remain unobtainable there.
Furthermore, Starship is anyway wholly inadequate to establish a continued presence on Mars. If it works fully l as well as promised, it might suffice to maintain a Lunar outpost.
Anyone who hopes to establish a sustainable presence off-Earth must look to O'Neill Cans.
That is not true. The tech required to maintain long-term living on Mars would be extremely valuable here on earth. It is directly relevant to many of our current goals for more sustainable lifestyles.
Much like the moon missions, the side-effect benefits that it encourages will likely end up making such a mission worthwhile for the tech alone.
I don't understand your criticism of starship though, would you clarify why you think it's not suitable?
Maintaining an adequate technological basis for continued survival on Mars requires, simply, many, many times more people than Mars could support. So, all the more tricky components and chemicals have to come from Earth. When those stop, the technological basis soon declines below the level that can support the population living there.
All the choices after that become very unpleasant, of questions about who gets to continue living. The supportable number declines inexorably to zero.
Yes, similarly to Mars, anyone living on the ISS would die not long after the last shipment from Earth arrives. Except for this similarity, I'm not sure what you mean.
Unfortunately nobody wants to live on Venus, in part because of that much denser atmosphere, so there's not much interest in making oxygen there.