Could you make a steel framing that in itself gives all the strength one would need and than use your method to build all the walls etc. Basically taking what you have and putting a steel frame around it. Sure that probably takes some away from your intent but it would certainly give prospective clients a better confidence in the buildings overall durability. I'm not saying this to criticize, I think it's a neat concept, but I hope maybe something I say might help spark an idea or something.
Isn't EPS Foam itself negative to the environment?
If I understand the idea my guess would be 'image'. People can't see it being strong enough. You could add something to make it give more strength but mostly gives people the warm fuzzy feeling it strong and long lasting.
I don't agree with your second point entirely. I think it's important if your going to try to do anything innovative or have a business of your own you have to align your goals with your passions.
I have a book which I recommend to anyone who wants to innovate. It's the best book I've ever read on the subject of creating and running an innovative company. It's called 'Innovate Like Edison' and is written by Michael Gelb and Sarah Miller Caldicott. It might give you some insiration to move your idea to the place that could make a difference.
I just had a thought. Is your system suited for making a quick emergency shelters like would be needed in disasters like Katrina or over seas refugee camps and such? Maybe on a smaller scale?