Elon submitted his final terms, there won't be negotiations, based on current public statements. As noted by others, the poison pill is not even in actual effect.
2) The valuation is not the only thing the board and Musk need to agree to. There are break up terms, ability to accept a higher offer if one materializes, liability in case of funding breakdowns, antitrust assurances, etc etc. So again, any leverage is useful.