An issue a game like DAOC will face is that when new items are introduced that can be purchased via currency - other currencies can start to lose their worth.
Is there any reason not to have a currency conversion NPC?
I don't mean just one or two, I mean all.
A one stop shop cash converter
You could charge a small fee for the service (plat sink) and then you just adjust exchange rates depending on the popularity/ease of access of any particular currency at any given time.
This is an indirect attempt at popularising zones that would otherwise be overlooked too because you could add different currencies to loot tables they didn't previously exist on.
I believe there are various means in place to convert certain currencies at the moment but not one NPC that will convert anything into anything.
Just a thought while bored at work ~