I really don't want to have to use the spreadsheet to fill out my wiki page. I have no idea how the wikia variables work, but if we can define them within the wiki page itself using a form, I'd rather go with that.
This solution would be fully contained in the wiki page itself. SemanticForms would make it a little easier to fill out. You could fill out entries in a form rather than edit the page source directly.
The first step is to design the template itself and then we can work on ways to make it simpler to fill out.
The only problem with using variables like this is that there are too many exceptions to too many rules to make this reliable. Take for instance the AC category. For those wearing Heavy armor, they just get what the armor grants. For those wearing Light armor, they get the better of their intelligence or dexterity modifiers on top of the bonus their armor gives. There are at least 2 classes that I can think of off the top of my head (Sorcerer and Warden) that allow them to use a different stat (Strength/Con/Wisdom, etc) for their AC. I wouldn't mind seeing these variables come into play, but it sounds like it will be a nightmare to implement and keep up to date.
You are thinking way beyond what I have in mind. Here's how variables would make the character sheet easier to maintain...
Right now, when you fill out the math section, you have to "show your work" to explain how you got at your numbers. Using variables, you could put "WIS" as your ability and then let the AC math template *look up* the modifier value from your stat block.
When you go up a level and change your Wisdom score to 16, you would normally go through all your math and update your ability mods everywhere to +3. All your powers, etc. With a variable, you would just change your ability score to 16 in your stat block and then the rest of the sections that depend on that ability modifier would be updated *automatically*. It would make the sheets a lot more reliable and more simple to maintain.
It doesn't make them fully automated.
Take a look at Finnian's math section for
basic attacks...
There are 9 powers here. I have to specify the relevant ability for each one, and then enter the ability mod for each power as well. If my STR mod changes, I have to update 6 powers in just this section alone. If my level mod changes, I have to touch all 9. If I were using variables, I would specify my STR, DEX, and level mods in one place (let's call it the stat block) and these tables would update automatically as the modifier values changed.
The Defenses template isn't designed to use alternate abilities for AC (in your example above) but this is one of the things we could change so that it did.