In purchasing a car with lifetime Over-The-Air software updates, there's good news and bad news...
The good news... You will periodically get new features that weren't available when your car was purchased. All Model S/X owners received the new navigation software last year, and will continue to see increased functionality in the navigation software. With other vehicles, it's likely what you have at delivery is what you'll have when you sell the car years later.
The bad news... User interface changes are inevitable - and always have trade-offs. Making the user interface look nice and cool could reduce in some loss in functionality. Some aspects of the UI may be easier to use - while others may be harder. And every time software changes, there's a risk new bugs will be introduced, which requires subsequent releases to fix the bugs (and more opportunity to introduce new ones).
Since purchasing our first Tesla in early 2013, we've gone through a lot of software updates - and while there are some aspects we miss from earlier releases, overall each major version is an improvement - and, over time, we get used to the inconveniences introduced in each major release.
While you can refuse to install the software updates when they are downloaded to your vehicle, at some point the Service Center may insist on installing the latest update before they service your Tesla.