Clean or Leave alone

[Dean Romig]

just as long as you don't use an abrasive...

My Dad was a coin collector and would soak severely tarnished coins in vinegar if I remember correctly.

[Roundsworth]

I also use vinegar to clean gnarly brass without abrasives.

[Joe Wood]

If they are just for display I suggest leaving them as is. Nothing looks more out of place than antique brass highly polished. With items such as powder flasks it literally destroys the collector value.