Man, the scythe chariot is one of the best peon killers ever. I laugh when people try to build towers as I'm raiding with SC. That entire group of peons dies together from 1 unit's attack. Or aim for his woodcutters or miners, they fall like flies.
Here's a trick I've learned when raiding with SC or war elles and your opponent has ground troops as protection; If you are not killing his peons, then have your SC/elles tear down buildings instead of attacking the gound troops. This keeps his infantry from surrounding your unit(and killing it faster) and you damage the building and his surrounding troops at the same time. This works especially great with 2 or more elles side by side. His ground troops can only attack 1 or 2 sides of your units and have to "stand in line" to get their turn.
Scythe chariots are also great for tearing down walls. Your opponent cannot repair the wall while you are tearing it down and if he sends cats to attack your SC, he helps tear the wall down.
dshea, to answer your question, I rarely ever made chariots before RoR and now it is the first superunit upgrade I get. And as Omnivac has mentioned, with no food involved to upgrade, it is an easy to reach and inexpensive upgrade. Usually when I reach iron, my available food goes for upgrading other things(alchemy, triremes, cats, etc.)