Modular Analog Circuit formula solver?
I think you have good idea, however it already exists in some variations. I found one example for BJT cascode stage: http://www.daycounter.com/Calculators/Cascode/BJT-Cascode-Calculator.phtml

But also, I'm encouraging you to make it on your own way for few elementary different topologies, having in mind this few points: 
1. it should be online;
2. it should be in pure javascript (not Java or Flash)
3. dialogs should be in schematic
4. SVG for that matter should be the markup language of choice

That's only my opinion. Good luck with this nice idea.