wrote...

What would cleaning a dirty plug do to the sound?

Remove potentially rectifying oxides. Also re-tighten the connection, making it
more secure / less electrical resistance.

I got a can of Cramolin last month and gave all my kit a good clean.
I was quite astonished at the crap that came out of the RCA sockets
on my 1979 JVC and 92ish Denon amps.I must admit I also had a go at
the pins and fuse holders on the mains plugs (as recommended by all
good Hi-Fi mags)but I was getting giddy from the fumes by then.

Can't say that I noticed any difference in the sound, but
it does give you a huge confidence boost to know that
all is optimal.

--
Ken
http://www.members.lycos.co.uk/buddyduck/