If silver is such a powerful weapon against spirits' Essence (and also against ghosts in Lockwood & Co.), why don't magicians (or agents) wear silver armor?
I imagine it would greatly reduce the stress of summoning since the magician would be protected should they make a mistake. (And even though it would be heavy and reduce speed and agility in a ghost hunting situation, if an agent were covered head to toe in silver they wouldn't really need to be fast because they'd be protected.)

Probably because silver is rather valuable and hard to come by. In the case of iron, though, that is a very good question.

maybe for agents, it's because it would interfere too much with their Talents?
with rapiers and stuff it's just enough to protect them, but a full suit of armor might hinder them from actually sensing ghosts. idk.