Just wanted to add my name to the list. I have done exactly what the OP is asking about - replaced my iPad Mini 2 with an iPad Mini 4 - and am very happy with the move. I've been waiting and waiting for an update. When the Mini 3 came out I, like many, laughed at the pitiful update. When the Mini 4 came out I was more impressed but happy with my Mini 2 still. Last summer I said when Apple update it again in the autumn I'll make the leap straight away. Nothing came. I wanted and waited hoping something would come but when the iPhone 8 and X announcement came and went with no mention of the iPad Mini getting an update, and nothing silently appearing on the store, I made the leap and picked up an iPad Mini 4 from John Lewis in the UK. They were offering an additional year's warranty (taking it to three years) and I price matched another retailer for a small (£8.64 or thereabouts) reduction. Bought a new case for it (my iPad Mini 2 case, at four years old, was dropping to bits) and a new super tough case for the Mini 2. The Mini 2 is now with a friend for them to use and my old-old Mini 1 which they had used previously has been handed down to my niece (or her mum and dad) to use.
If Apple update the iPad Mini again I'll be very torn as to what to do. I don't think we're going to see anything until at least early next year (March/April) and even then I'm not sure. I do have to wonder if Apple have abandoned the iPad Mini line - although you could have thought that about the 4-inch iPhone but then the iPhone SE came out and I love mine.
A