I honestly don't see the problem. If you never use the internal storage then yes, it will never wear out, but then you're not using it so why even have it? You use an SD card, it wears out, you get a new SD card, and repeat, meanwhile the NAND remains pristine... for what?
If you use the internal storage and it wears out early and you need to switch to SD cards you are not any worse off than you were just using the SD cards and ignoring the internal storage; plus you get to take full advantage of all the benefits that come with using internal storage vs external cards. And there's not really a risk of it breaking anyway, so there's that. In the choice between "use internal storage and risk wearing it out" vs "never use it, only use external SD cards" the answer is obviously "use the internal storage until it wears out"
That being said, the flash is rated for tens of thousands of writes, and between proper wear leveling and the fact that the average use case doesn't see a lot of writes to the "OS drive" as it were you shouldn't have anything to worry about. This may change with the Pyra: the Pandora's flash only stored the OS files, with all programs and (presumably) file storage on SD cards. The Pyra has a sufficiently large internal storage space that I can foresee the use case changing and people installing stuff and storing files directly. Whether this changed use case will make a difference or not I can't honestly guess, but I would stake a small claim on the Pandora being safe to use.
@ahahah, your problem is different; you probably had a bad unit. It happens, no process is 100% perfect, it failed early, unlikely to be a result of excessive writes, it was just bad memory.