I don't want to sound harsh, but charging more for a theme because it's coded "well" or uses xyz technology is ludicrous.

Themes should be coded well. Period. I don't care if they use Backbone. Do you think the average user of WordPress cares about the technology behind the media uploader? No, they care that it works.

Well coded themes should be a standard. You wouldn't pay more for a car because it has a windshield, would you?

Don't get me wrong, I would pay a $100 for a theme, but it better look good, be easy to configure, and conquer the niche I'm using it for.

Just my 2 cents.