if u are just using it for light surfing, iPad mini 4 should still be able to tahan for another 1 to 2 years indeed. becos my iPad mini 2 also is used for more than 5 years now and it is still fine for light usage.

However, if u are into gaming for other heavy duty tasks like AR etc, upgrading to mini 2019 should be worth it too.
It is 3X cpu speed of iPad mini 4 and 9X better graphic also.
Haha but I dun have any fast charging equipment. becos I am not really into fast charging. I am using my 10w iPad charger to charge my iPhones so far so good, do not really need fast charging.

For iPad mini also, if it comes with 10w and above charger I am fine with it. hahaha.