iOSification can come in two forms: aesthetic and functional. The aesthetic changes don’t worry me in the least. It’s the possibility of the eventual removal of macOS features that set it apart from iOS that would be concerning.

Consider adding Ars Technica to your list. They aren’t specifically focused on Apple news, but a couple of their journalists do routinely offer some fairly balanced reporting on Apple affairs. Plus, their Android expert is constantly comparing Android devices to Apple devices… and he very rarely gives Android a total win in any given comparison. I think it’s quite amusing to read, actually.

Apple tech specs online says that it’ll support up to 16GB – but sometimes their spec sheets lowball the actual compatibility. At any rate, you can be sure that it’ll accept at least that much. (Source)

And maxing out the RAM is always better for performance, regardless of whether you’re using macOS, Windows or Linux. (This is doubly true with older hardware, such as what you’ve found.) The question isn’t, is more RAM a good idea… it’s, is more RAM worth the cost. And with a 16GB RAM kit for that system going for about $16 on Amazon, I’d personally say go for it. (Double-check that I’ve found the right link for you, of course, just in case.)

In your case, I would assume that you’re looking to actually use your iPhone 12 mini, after replacing the battery, as opposed to seeking out the actual trade-in value. Would it be worth it to you? Honestly, I suspect so. If you have a particular affinity for your mini, possibly because you just can’t abide the larger form factors, then you’re pretty much stuck with a 12 or 13 model, as there is no 14 mini and there almost certainly won’t be a 15 mini; Apple has moved on from the smaller form factors. And given that an upgrade to a 13 would be a lot more money for a lot less relative value, I personally think you might reasonably find it worth the few dollars that it would cost to replace that battery.

Oh… but don’t do it through Apple; do it through a reputable third-party. Way less expensive, and likely a lot faster.