I don't see the value in upgrading parts of my phone apart from a failing battery. And if you read it again, I upgrade because my sons phone is 4 years old, and changing the battery is no longer worth it anymore to me.
But I suppose it's better to just jump on semantics instead of trying to understand the whole of the post.
Admittedly, you plus your son get 4 combined years out of the device. It's an unexpected way to count, but it works. And since you were talking about buying new devices, I took it as a context where that's what the word "upgrading" means too. I wouldn't speak of open-source or third-party mods to the phone as "upgrades", just... "modding". Anyhow. Sorry for skimming.
But I suppose it's better to just jump on semantics instead of trying to understand the whole of the post.