You can find out why I created Navception in the Description under Navception's Inception, but let me tell you why I like what I created.
First, Navception does everything I hoped to accomplish with writing it. I can make a small menu that shows up by itself in a sidebar, and then I can embed it as a Nav Item into the Main Menu with little effort (not including the effort used to create Navception). Now when I update that sidebar menu, guess what, the Main Menu benefits from that update!
Second, I learned a great deal about the WordPress Menu system (which is begging to be updated). For example, check out wp_nav_menu_item_taxonomy_meta_box, I was able to tap into that function to have WordPress create the Nav Menu box in the Nav Menu editor for me. It's pretty wild!
Regardless, you should try this plugin, because even though you might not need it now, if you do in the future, you'll know what to use: Navception!