I rather like this article by blogger David Jays. Smell-O-Theaterama. You are THERE.
He mentions the scents of toast and thyme and blood... I have to admit, the last time I smelled something at a play, it was the actors sweating through their shirts in a claustrophobic black box theater... but it was good clean sweat, well-earned through hard work, and I didn't mind it.
I draw the line at spit, though.