I think you should add diagrams of electronic components ( diagram of resistor, diagram of capacitor.......) so that it's possible to make circuit diagrams in the app.
Here's a link with the most common ones( http://www.zen22142.zen.co.uk/Prac/symbol.htm) if they would all be added then I'd definately use this app a lot more.
Oh and also there isn't a single app out there which allows making circuit diagrams easily so it would really be worth it I think.