The display is exactly the same in the 2, 3 and 4. The only "carrot" to me is 2GB of RAM in the 4, vs 1GB in the 3. An update to the mini with at least the A9 chip, which is a minimum requirement for things like ARkit, would carry it at least another 2 years. As it is, all the current iPad mini models are getting a bit long in the tooth.
No, the display is not. It was dramatically upgraded for the 4. However, I agree, the Mini is long in the tooth. The shame is that the Mini 4, like the 3 and 2 before it, was long in the tooth when introduced. Each was roughly a generation behind the 9.7' iPads when introduced.
Here's some comparative comments from DisplayMate's tests:
Early 7.9 inch iPad minis in 2012 – 2014
The much anticipated smaller 7.9 inch iPad mini 1 launched in 2012, but the mini’s display performance has always lagged the full size 9.7 inch iPads by 1 to 2 generations.
In 2013, the mini 2 was upgraded to a Retina Display but still only received the lower 62 percent Color Gamut, which also continued for the mini 3 in 2014. The mini screen Reflectance was even higher than the full size iPads. The iPad mini was treated like the runt of the litter, but it has now found favor and been transformed into a beautiful leading edge display on the new iPad mini 4…
The iPads for 2015
For 2015, all of the current iPad displays have all of the enhancements mentioned above. The iPad Air 2 continues on as the current 9.7 inch model,
the new 7.9 inch iPad mini 4 has received a slew of major display performance improvements, and there is the brand new iPad Pro with a much larger 12.9 inch display that is intended primarily for professional and advanced imaging applications (and promoted as a laptop replacement).
iPad mini 4
The iPad mini 4 is close to being a textbook perfect LCD display in all of the Lab measurements and viewing tests. Among the iPads it takes first place and is marked Best in every single test category except Contrast Ratio – where it has a Very Good but not the highest Contrast Ratio of 957 in 0 lux (because Apple didn’t provide a Photo Aligned LCD like on the Air 2 and Pro).
Among all existing Tablets of any size, the iPad mini 4 takes first place and breaks performance records in many of the most important test categories including: lowest screen Reflectance (2.0 percent), Highest Contrast Rating in High Ambient Light (225), a near perfect Log-Straight Intensity Scale and Gamma of 2.22, and the highest Absolute Color Accuracy (Average/Maximum Color Errors of 1.9 and 4.2 JNCD – tied for first place with the
Microsoft Surface Pro 4). If Apple hadn’t intentionally made the display’s White Point so bluish (7,109K instead of 6,500K) then the Color Errors would have been even smaller.
...and from an earlier DisplayMate test:
iPad mini 3: A Major Disappointment
The iPad mini can only be described as the perpetual Runt of the litter… Originally spurned, then introduced (in haste) in 2012, it was a mini version of the older 2011 iPad 2 with a 1024x768 resolution display and a reduced 62 percent Color Gamut, when the full size iPads already had a 2048x1536 Retina display with a 100 percent Color Gamut. In 2013 the mini was given a Retina display, but remained with a reduced 62 percent Color Gamut – the only current iPad or iPhone without a full Color Gamut. Now, in 2014 the new iPad mini 3 still only has a 62 percent Color Gamut, plus it was denied the new enhanced anti-reflection coating and bonded cover glass of the iPad Air 2. So in addition to washed out, under saturated and distorted colors (red tomatoes, fire trucks, and Coke cans look a bit orange rather than deep red, for example) it continues with a moderately high screen Reflectance of 6.5 percent, almost triple that of its favored littermate, which further washes out its image colors in ambient light…