I haven’t ran into the lower topic limit yet. Absolutely agree that topics should be long enough and worded well enough to represent the contents of the thread without having to read the thread. Can short topics do that? Possibly. One good word can do a better job than a sloppy sentence. If the writer puts effort into the topic, there’s no need for a limit. On the other hand, even a 30 char minimum limit won’t help if the writer is careless. Example: “New topic subject… Pleeeaaasseeee” is a bad topic. It doesn’t tell me what the thread is about. Its character count has nothing to do with it.
I don’t have any strong feelings either way regarding the limit, it works for me as is, but what I would do if this was entirely my forum is to set the character count lower limit to something which should only prevent accidental new empty topics, like 3, and only raise if it practice shows that there’s a need, not the other way around.