I think it just comes down to individual needs and wants. I've had all iterations of the iPad and got a new 4 and Mini yesterday. Other than the screen being more yellow than I'm used to, the 4 is great. Is it significantly better than the 3? No. But I don't game, and someone who does may think it's fabulous.
I was convinced the Mini was going to be the holy grail for me. I was very disappointed in the screen resolution and didn't fully realize how accustomed to retina I'd become, but I can see where the Mini has its uses, and the form factor is great. For instance, I'd be more likely to throw this in my purse and tolerate the lower resolution just for convenience. I never do that with the full-size one. I probably wouldn't try to create a spreadsheet on the Mini, though, and I thought a lot of websites looked pretty bad in comparison to retina. And I won't be reading books on it at home, for sure, but it would work fine on the road. But...I thought even the iPad 1 was the greatest thing since sliced bread, so if I were stuck with only a non-retina tablet for the rest of my life, I'd live and live well. I still look forward to the Mini with retina. That is what is missing, for sure! I'm still not sure if I'll return the one I have now. It kind of grows on you. I'm more likely to return the 4 because it's so similar to the 3. Ask me in a week if I've returned either...I probably will be happily enjoying both!