I don't think that there is a foolproof method for differentiating yourself from other ThemeForest authors. If there was (like adding lots of options), someone would be using them and making them not so different.

While it is a shame that the market for one-off themes is overwhelmed and dominated by a marketplace that functions like this, it's generally only seasoned developers that voice concerns. The average consumer won't understand all of the nuances between a well thought out theme and one that adds additional kitchen sinks onto the existing one. This isn't necessarily a bad thing, as different users have different needs and wants. Being the most WordPress standards compliant is not as important to most users as having the look and options that they want on their site, best-use or not.

I'm working on a theme framework company myself, and the hardest part for me is going to be hitting that sweet spot between pleasing the developer crowd and the end-user crowd. If anyone here has a silver bullet, I'm all ears :)