Should I be worried about this?
Yes. Your local network should be as secure as you can reasonably make it. More importantly, your ISP should be responsible for the pipe between your local network (which is your responsibility, and includes access to your devices), and the Internet (which is more or less the Wild Wild West).
For all the other answers regarding "it's only a problem for people who are close to get it", once it gets leaked onto the Internet, all the people who are already close enough - and their bored teenage and preteen kids - will be able to find that wifi password.
Or is there something about router wifi passwords that makes it ok to not hash the password?
Your question is based on incorrect founding assumptions. A web site should indeed use a password hashing algorithm if they are going to store passwords with which to authenticate their users; i.e. whatever their user logs in with.
In your case, the ISP is storing something your are NOT logging in to THEIR web site with; the question is not the manner in which they store it, the question is how you stop them from storing it entirely, since there is no need for them to have it at all.
Note that this is triply true for a wifi password - unlike good storage encryption passwords, where if you lose the password, you lose your data, if you lose your wifi password, you just reset it on the access point/router and your devices, which has the side benefit of rendering everyone else with it unable to get in anymore (if you do it right).
If there is a problem here, how can I pressure Spectrum to properly secure their passwords?
How do you pressure Spectrum? You go to another ISP that doesn't keep your wifi passwords, and tell Spectrum why you're leaving.
How do you solve the problem of their having a password they shouldn't? You buy your own access point, or access point + firewall, or home wifi router/"firewall", change the Spectrum wifi password to something long and random, then disable the Spectrum wifi completely, using only your own device, ideally behind your own firewall to protect you from Spectrum.