It would be nice to reduce the spam but I don’t think it would be effective. You can roll a new Alpha and fly them to Jita in a couple of minutes and I have no doubt most spammers are using disposable Alpha accounts. They used to use disposable trial accounts.
The best solution is to ignore them - monitor a different chat. The reason spam exists in-game and in the real world is that it works - they make a lot of money from people who believe Jita local is populated by philanthropists.
If you ignore local chat in Jita, the probability of missing anything useful is vanishingly small.