Interesting comment about Paul Simon's songwriting Peter. A lot of my favourite songwriters have this characteristic; Townes van Zandt, Guy Clark, Lyle Lovett, Steve Goodman, John Prine, etc. I wonder if they think about it as conciously as Paul Simon obviously has?
I can't put my finger on any one thing that makes a song stand out. Sometimes it's one verse or line in a song that captures the entire mood. An example of this, for me, is John Prine's Paradise:

Some times we'd travel right down the Green River
To the abandoned old prison down by Adrie Hill
Where the air smelled like snakes and we'd shoot with our pistols
But empty pop bottles was all we would kill

I mean, hearing the verse, you feel as though you might have been there yourself.
By the way Seed; thanks for refreshing the thread. I was out of town and sort of forgot about it.
Dave T