SimpleRockets 2 is supposed to be a simple game, it's in the name, but it's not. It's just not a simple game.
This has to do mainly with the menus as there are way more than you'd expect for a simple game. So many things to change, so many things to do, so many menus. It's just all in your face.
The way I'd go about reducing the clutter of the menus and making the game simpler is to add a "Advanced Mode" into the game's settings. People would start with the mode disabled, which would mean they would only see the most necessary tools/options. They wouldn't have access to the tinker panel, custom color creator, part connection tool, advanced part options, lift vectors, part grouping, and seamless edges until "Advanced Mode" is enabled.