This seals it for me. Just my personal opinion here, but if I were $20K under water on a car loan I couldn't imagine even considering purchasing a new (or used) car just to get a couple of new features.
For what it's worth (and for the record this is a terrible bit of analysis to perform from a financial perspective), I doubt any lender would issue you a car loan with that much negative equity. Most lenders require a down payment because they know that your car will be immediately worth less than the sale price and they don't want to carry the negative equity should you default on your loan.
My suggestion (again, FWIW): ride it out with your current car. Use some of the $20K to buy shares of TSLA and revisit this whole thing in 3-5 years when the next refresh S/X drops.