Your theory is sound, however there are much, much more variables to consider. Firstly, cables are an important variable to your sound. While there may be a lot of hype, which cable you choose to use can affect the sound. Depending on the components, (or cables), the length could have an effect as well.
Then you have to consider the connection. It is true that the connection is very important, and soldering is only one type of connection, not an elimination of such. A crimp or screw on type would be another that often works better than a solder joint. Keep in mind that the device used to make the connection, such as an rca, will also have some sort of connection (usually a solder) on the component, and the quality of the connection is a variable. While a high quality crimp rca (such as a wbt 108) will always outperform a radio shack soldered, your milage will vary. If you were to hard wire your components together, your milage would vary depending on how many connections you were to eliminate, the quality of them, and of corse, which wire you use.