>2/ Regardless of what version of UBI you personally support, it is probably not a good idea to give money to those who don't need it.
Wrong. The system doesn't work if you don't give people to money who don't need it: the administrative requirements of assessing who and who doesn't need it, and then policing all this, is just too high. This is the reason UBI was invented in the first place!
It's very simple: you give the same money to everyone, even if they're a billionaire. To make up for this, you raise the taxes a commensurate amount on the people who don't need it (and more for the really rich people, because the idea is wealth redistribution). So someone making $100k, for instance, obviously doesn't need a handout, so you raise their taxes that same amount so they're paying back in taxes what they're getting from the UBI, and netting zero. It's much easier to do this than to have thousands of government workers auditing everyone to make sure they aren't "cheating" by receiving money they're not qualified for, which is what we do with current welfare schemes.
>Sooner or later people will realize that what they really want is tax/benefit reform
No, tax reform doesn't do anything to reduce the administrative burden of current welfare systems. UBI does. Less money you pay out for unnecessary government office workers is more money you can end up giving to people in need, and society will be better off with those government workers finding more productive professions which might actually generate more wealth and taxable income, instead of just being a drain on taxpayers.