So first of all, I strongly disagree with the notion that great medics are strategy at all - that's a tactical idea. Quibble quibble.
Touche. I stand corrected.

I now assert that it is a basic piece of
tactics that every player should be familiar with.
Simply put, the scale is all wrong. For example, suppose you have to choose between two different ideas for warfare - you can have siege units, or you can have super medics. Is this even a choice? Couldn't you just as easily tell beginners to disband the Great General when he spawns, without much adverse effect?
Put another way - Sisiutil's beginner guide has 15 chapters; I'm essentially trying to pare that down to the seven plus or minus two ideas that a novice needs. How many different ideas do you suppose are in that guide that are the same size as the idea of a super medic?
Unless I'm gravely mistaken, Great Generals and super medics were introduced in Warlords - they aren't part of the core game. I find that to be a pretty compelling argument that they aren't central enough to the game to be worth discussing at this level.
Were I outlining (in my own humble opinion) basic warfare strategy in Civ4, it would be this:
1. Make about half your stack siege units, and the siege should bombard and attack first.
2. Include one great medic with your stack, who should never attack.
3. March your stack straight at the enemy's strongest point, crushing everything you pass on the way, then pause until your stack is healed.
4. Repeat step 3 until you win.
I admit that things usually look simpler once you've learned them, but that doesn't look like an overly complicated strategy to me.
As for the relative importance... while I agree that great medics are not as important as collateral, I would argue that they
are as important as things like early scouting patterns or settling blocking city locations. Maybe it's just the warmonger in me that makes me see this as such a powerful concept though.