I have to agree with MrDRMorgan. What one hears from "professional auto advice givers" (for example, "Car Talk" and those like them) on the subject of "repair vs. replace": if the car is in decent condition, it is *always* cheaper to keep and occasionally repair your older car than to buy a brand new one (sometimes by a significant margin). This is because of the rapid depreciation on new cars the first few years.
Now, keeping an older vehicle means that you don't get new "advances" (say, a 1999 Chevy Silverado pickup truck doesn't have side curtain air bags, or Automatic Emergency Braking, or collision avoidance (backup/back-over radar) which many 2018 vehicles have now. So you decide to pass on that (or not).
Also, it makes a difference if you are a single person (by that, I mean living alone) or you have a multi-person (close, "significant other" or family) living arrangement that shares vehicles. I have the latter arrangement, and having a vehicle that does 60-80 miles around town would be just fine for us, since the other car is very long-range. One of us is *always* driving less than 50 miles during any given day. A single person wouldn't be able to get away with that as easily.
Personally, myself, I would probably jettison (sell) a Spark EV when I could get a 110+ mile range EV for $10K or so; until then I'd just stay with "Sparky". There's virtually no maintenance (tires, windshield wipers up to about 60K miles, then maybe a transmission fluid change). I wouldn't replace the battery (for $5K-8K) if I could buy a 2020 EV with twice the range for around 10K. If used EVs were selling for $15K, then I'd have no problem dropping $5K into the Spark EV for a new battery and transmission fluid flush. I'd figure to get another 5-10 years out of it - cheap at $5K. To me, it's not what the car is worth if I sell it, it's how much would it cost to get a replacement vehicle, and if the extra cost gets me 'enough' extra bells and whistles that I thought it was worth it.