Warning!!! Long post and I think I may have rambled on a bit...
Here's just a few thoughts that I've been having over the last few weeks, please note that I'm by no means any amazing player but there are just a few things that I have noticed.
So what people usually do nowadays is find a unit that works well, stuff it full of equipment that does the job well too and then spam throughout their army. In the past I when I was told that this would make an army too "one-dimesional" I didn't understand how this could possibly be. I mean if you have loads of awesome stuff in your army wouldn't that make your army awesome too? Well that's the trap that most "netlists" fall into.
What one-dimensional means, is that every time you set up your army to play a game, you're always going to do the exact same thing no matter what, army-wide. This makes your list as a whole far too predictable, and so there is no scare for your opponent as everything is doing the exact same thing. While your whole army is working in conjunction with each other to do whatever they do best (e.g. meltavets in chimeras), because they all contribute small parts to a greater whole and that greater whole is always the same thing, then your opponent is always going to see what you're trying to do and perhaps be in a better position to adjust and stop it. It also, releases pressure off of your opponent and could make them complacent, rather than being on edge and being forced into silly mistakes and bad tactical decisions.
So let's take a look at an example, below is my Imperial Guard 1750 pt list: