If I had a choice between e.g. $3000 monthly for working and $500 for staying at home, it would feel very different from choice between $3000 for working and $0 for staying at home. I could probably translate the "very different feeling" to better position at negotiating either higher salary or better working conditions.

It's not obvious whether I could translate it exactly to $3500, or whether the additional money would be split between me and my employer. Please note that the labor market behaves a bit differently from typical markets, because when you pay people more, their free time becomes more valuable. For example, if you paid me 10 times more money than I make now, a likely consequence would be that I would work for you only shortly, and then enjoy an early retirement. (An effective altruist would keep working, though.) By increasing the market price, the supply can go down. So in some circumstances it could create a spiral of skilled people demanding more money, then leaving the labor market soon, which would increase the salaries of the remaining ones, etc.

Not necessarily. That's why I brought up the example of basic income serving as a permanent strike fund to help employees demand higher wages. Employers can respond by meeting their demands, and/or automating more quickly, etc. Then society can respond to increased automation by increasing the basic income. Or not. I won't talk about society's transition into a gift economy here because that would take too much space.

I know you're trying to paint Basic Income as a subsidy to employers, but it's really not like the Earned Income Tax Credit. At all. I'll continue this in the LukeASomers thread.

in the proportion it was given to workers, it would be a subsidy to their employers.

No. To illustrate, look at the starting point of the aforementioned subsidy to employers: the Earned Income Tax Credit. You can only make use of the EITC once you are employed, so all else being equal, the EITC contributes to the idea: "If you don't work, you starve." I may then feel pressured to work at McDonald's or Walmart. By contrast, Basic Income exists external to the market, serving as a base amount for everyone to live on. Since I don't have to worry about starving anymore, I now have more leverage in choosing if/where I want to work. Any amount I earn on top of the base amount is of my own volition for luxury items not needed for my survival. If I later want more money and my employer resists, I can use the basic income as a strike fund.

Unemployment benefits would be sufficient to obtain these effects without transferring wealth from the taxpayers to the employers.

Three things. First, you seem to be forgetting my earlier point regarding staying power. Even if you rally society today to support your targeted "unemployment benefits" (I put it in quotes because I know you mean it in a welfare context that is wider than merely unemployment compensation), your welfare solution is still at risk of being stigmatized in the future and then cut by politicians. Basic income for everyone avoids this risk, and will have much greater staying power.

Second, you seem to be under the impression welfare is handed out like free candy. In reality, welfare can be a pain in the butt, whether it's the intrusive paperwork, stressful delays, or the threat of fines and probation. Basic income bypasses this mess.

Third, you keep suggesting "taxpayers" and "corporations" are two separate things, even though corporations pay taxes too. Yes, corporations are quite adept at avoiding taxes, which is why tax reform also needs to be a part of this discussion.