The problem is that the increase in wages will necessitate higher prices to the point at which the UBI is not longer sufficient on its own, so the above mentioned effect falls off, and you find some sort of equilibrium at which poor people still need to work to survive.
It's not crazy to imagine the long term impact being what you suggest though. Right now you need, say $100 paychecks to survive. In a universal non basic income, you might only need to earn $50 + your UnBI. The cunning capitalist observes here that the poor need fewer wages to live and so they get... fewer wages.