I'm running on 2021.24.28 (latest in the stable, non advanced/bleeding edge update stream) and it works fine for navigation and music streaming (and app connectivity to pre-heat/cool, etc). Maps can take a bit to load when adding a new route, but as the car is driving I never see blank tiles. Menus have become less responsive with each update, but still functional. I drive my wife's MCU2 from time to time, and honestly, while I see the difference in responsiveness, it's a non-issue for me. I more notice the acceleration difference and lack of sport+ suspension than the MCU difference.
Your comment made me think about how much would I be willing to pay for MCU2. I started with, what if Tesla offered to do it for free with FM radio. Hmm.... honestly, I'd probably do it just to increase the resale value. Then I thought, how about $100? Probably yes. $200, still yes. $300, ok. $400 - $500, maybe. Above $500, no desire whatsoever. Next year, when my Taycan CT Turbo will finally come to replace the Model S (have been waiting for almost a year now), I will inform the next owner they have the option to pay $1,500 or $2,000 for an updated MCU2 if they so desire (maybe they can get a credit for MCU1 recall since Tesla denied my claim after self-repair of emmc). Me spending the money now would not raise my used car value by the same amount, and since I don't see the value in functionality for me, there is no reason to spend the money.