A balanced diet makes your people healthy, thus the varied food resources. This has historical validity. It wasn't until people began eating a diet of largely wheat that many health problems cropped up (pun intended, twice) in early populations in the middle east. Man is an omnivore and requires plants, meat, starch, etc. to be a healthy critter.
I prefer a quantative vs binary system for strategic resources any day. As noted, you HAVE to go to war in civ3 to get stuff. This should not be necessary. You should be able to choose between 3-4 paths towards victory, each requiring a different chain of resources. Maybe a tech/scientific civ, moving toward the goal of interplanetary travel? You'll need lots of metals- copper, titanium, etc. Economic powerhouse? You'll need gold, silver and platinum to be able to build those all important monetary systems. Warmonger? You'll need iron, coal for making steel, lots of copper for electric components for your weapons systems - and of course, oil. You would always have some of all of these in your empire - but never enough. Then you are faced with interesting decisions. How should I treat my neighbor? Will he have stuff to trade for later? Can I actually get in there and conquer those resources, being a peaceful civ? Hmm, those desert mountains in Mongolia look interesting. Will Khan have copper and titanuim to trade a couple centuries down the road?