For starters, it affects how easily they could raise cash by borrowing money, during a time when they desperately needed capitol.

The problem with that legal theory is that Musk insisted at that time that Tesla did NOT plan to raise capital: https://www.cnbc.com/2018/05/02/tesla-ceo-elon-musk-continue...

Perhaps that was decided because it was costly?

Saying you do not plan to do something, does not mean that you won't change your mind if circumstances change in the future

so for starters it's some unquantifiable handwavey opportunity cost

Tesla also have some convertible bonds out there that can be converted to stock if the stock price is above a certain number, but otherwise I think Tesla has to pay it back in cash.

https://www.cnbc.com/2018/08/08/elon-musks-tesla-stock-boost...

Stock price caused Tesla be valued less. Bonds, stock options, add more collateral to cover loans, sold to cover loans....?

But apparently Tesla was valued less because of these actions at that time.