For me, there is no device that beats an iPad mini for prolonged consumption (mostly reading/browsing) and quick productivity tasks. It gets more screen time than any of my devices (iPhone, iPad Pro 12.9, MBP, Mac mini, TV), and with weekends maybe even more than my work computer haha.
By far the main reason it gets the most use for me: its size. It has a bigger screen than a phone, but still small enough to grab and read with one hand (a pop socket helps). This enables me to rather comfortably use it all around the house for hours on end. Bigger iPads simply cannot effectively fill this role for me, regardless of their better specs. Sure, I’d like to pay for higher specs on the mini if I could, but the specs are secondary to the size for me. It only needs to perform decently, which the mini 4 does.
But the price does need to match the performance, and the projected remaining years of support. I made sure to wait for a good sale before I bought my mini 4, since I bought it later in its life.
I bought the outdated mini 4 not only because it’s more useful to me, but also because I felt it was important to vote with my wallet. By buying an outdated mini, not trading up to the bigger “better” iPads even at comparable prices, I, a regular consumer, was able to send Apple a message in the only language they understand that there is indeed demand for an updated iPad mini.