The decision to close Wellington's trolleybus system is obviously going to
live on as a lesson around the world. The author of this excellent
transport channel covers all the issues well. Talking of costs, ironically
Wellington got rid of a system that had the lowest whole-of-life costs of
any electric transit system and replaced it with one (battery buses) with
higher costs and less reliability. If only they'd made that modest
investment in maintaining the infrastructure over the years, they would
have saved themselves a lot more cost later.

https://www.youtube.com/watch?v=xxqnkLcMn4g

Here, by contrast, from the same author, an interview about how the city of
Tallinn, Estonia, decided to keep and expand their trolleybus system
instead of close it. Note the comment that trolleybus substations can be
used by a future tram system if required (vice versa also applies, e.g. in
Prague).

https://www.youtube.com/watch?v=3nm6eBzV0SU

Tony P