I took the plunge today, the wife will take my current Mini 2 and said I could be a Mini 4. Can't wait for it to arrive from Amazon.
I also got the Logitech keyboard headed this way, I sure hope the split screen is worth it... I think that's all I'm gaining...
There are hardware changes which will impact how you will use your device. For instance I tend to use safari quite a bit throughout the day. After a couple of heavy apps or just too much time in another app the webpages in safari would refresh on my Mini 2. This occurs far less often on the Mini 4.
Small improvements like the speaker also don't get mentioned much but you begin to notice these things when you start to use the Mini 4.
Another small thing is because the A8 is more efficient, they were able to make the tablet thinner, largely achieving this by slimming down the battery about 20 percent or so.
Normally this is a bad thing and yes of course who wouldn't want their battery to last a little longer? But the nice thing is because it's a smaller capacity, it charges faster too. The efficiency gained with the A8 still allows for about the same battery life as the Mini 2, so it's not all bad.