Cables 101, new student, first question

I have a simple question if I can get it worded correctly. For simplicity, let's say my system has four interconnects in a "stream," all from the same manufacturer, some from the top of the line and some from the bottom. Example: Wireworld's Eclipse 8 line, four different versions, the least expensive starting at $325 and the most expensive starting at $1700. In general, will the system's sound be defined by the weakest (cable) link in the chain, in which case all the more expensive cables are a waste of money? Or will a mix of cables that includes some really high-end ones sound better than a consistent run of the cheaper stuff? 

To put this a different way, if I'm buying a couple new interconnects (again, for simplicity's sake from the same maker), might buying better ones improve the sound or will I not hear a difference until I've replaced them all? (Here's the stream analogy: if I put a dam upstream, the flow in the entire river will be reduced.)