Ooh good thread!
Personally, I really like political songs, (caveat: provided they are good, that is). I'm not a massive fan of Billy Brag or the 'protest song' movement (whatever that is).
But, quite a few of my songs full under this umbrella, and I can think of some real corkers from big recording artists just off the top of my head:
Living for the City by Stevie Wonder
Sign O The Times by Prince
Anything by Rage against the machine, most notably killing in the name
Hell Broke Luce by Tom Waits
I could probably think of many more if I put my mind to it. But I also agree with your 'show don't tell' rule - but I would say it applies to all writing, not just songs, and not just social commentary. The most powerful words (in my opinion) are the ones that lead you to the writer's point without ever bashing the idea over the head.
For me, what works best is to try and develop a personal angle. Either treat it as a discussion (in a Paul Simon kinda way) or some kind of relationship issue. In other words, any way you can humanise your message is good. But this shouldn't be a problem, right, because politics and society are all about people!
For those who are interested, a couple of my songs that fall into this category are laissez-faire (neo-liberalism)
https://soundcloud.com/anthony-lane/laissez-faire-produced-byand North of the Woods (9/11) (rubbish vid of a pretty rubbish open mic rendition; proper recorded version is nearly ready to share)
You should share your political songs with us Todd