CI is very simple to learn and to use. But, there is still a learning curve. Not much of one to be honest, but there are still some things you have to understand. The docs are excellent and the tutorial should get you going pretty quickly.
Your spaghetti code, how extensible or maintainable or DRY will that be for any level of real complexity (not a contact us form). Have you validated the input data, have you cleaned the output data, have you got xss protection, have you separated the code from the html, have you put your business logic separately in a model away from the control logic? No, you have not. But with CI all this is done in a few lines using the MVC architecture, the framework tools and utilities, all cleanly and quickly and with no fuss.
I have created quite complex and extensive web apps using just MVC, the use of HMVC adds a non-default layer on top of the framework and increases the complexity and learning curve for development. I would suggest you master MVC before trying HMVC.
