Hi Bilych, I understand your concerns. I personally am not too worried with mileage as a lot depends on how the car was driven and how the battery was cared for; however, with an older i-MiEV there are three concerns -
1. Rust, if the car was exposed to salt on winter roads - I personally have no experience with this topic.
2. Battery capacity - can be measured with an app (such as CaniOn on Android and a number of other apps discussed on this forum) and bluetooth genuine OBDLink LX or MX OBDII adapter, or else with a Mitsubishi MUT3 diagnostic. To last you for the next four years I would look for a car with >35Ah but I suspect all the pre-2012 cars you are looking at will have a lower capacity. Perhaps others with pre-2012 experience can comment on the relationship between age and mileage and capacity? We have a number of threads on this topic; e.g., http://myimiev.com/forum/viewtopic.php?f=23&t=4014
3. On-Board Charger
/ dc-dc module. Unfortunately, there is no way of predicting if and when this module will fail. Its replacement cost is prohibitive but some forum members have been successful in repairing this module and we have a very detailed thread on this topic which is a worldwide technical collaborative effort. Most cars have at least one Achilles' Heel, and this is the i-MiEV's. As far as I know there is no way of predicting the imminence of its demise.
Did I understand you correctly that you're only planning on putting on 24K km in the next four years or is that 24K km per year?
Hope others can jump in with some some words of encouragement.