Arrangement of components on rack

Make sure your amp, or anything tube, has adequate ventilation. Keep your main source close to preamp (for shortest ICs). And be aware that phono preamps may be sensitive to adjacent components. I had a problem with hum in my phono pre from other components too close. 

You mention dusting, but not cleaning contacts. That is the reason things sound better, simply unplugging and plugging in again swipes and cleans things a bit. Cleaning with any contact enhancer, or even plain alcohol, will be even better. Use something like NPS1260, take it to a whole new level.

The act of disconnecting and wiggling wires around upsets their equilibrium resulting in a sound that is etched and grainy. Depending on your ears and system this might combine with your meager cleaning to produce a feeling of improved detail. Clean and give the system a while to settle in, then you will hear improved detail.

Where components go, and where wires go, definitely does make a difference but this is a judgment call you just have to experiment to find what works with your particular components and setup. In general it is good to keep sensitive components like a turntable or phono stage away from great big transformers. All the wires, not just power cords and interconnects but all the wires, should be kept as far away from others as possible. When they cannot be kept away it is better they cross at 90 degrees than run parallel.

But what matters even more is vibration control. Biggest bang is if you can put all components on Townshend Pods. Except speakers, where Podiums are even better. As for wires, they should all be suspended and isolated from vibration. The improvement compared to wires in a tangle laying on the floor is not subtle! Do all these things and it will be like you got a whole new system.

Since you will be doing this right now, and since Townshend cost big bucks, here’s what you can do right now for next to nothing. Use Q-tips and 100% cotton cloths to clean all contacts with alcohol. Do not try to go inside the IEC or RCA but do clean all the outer exposed bits, including the little prongs inside the IEC receptacle on the component. Put everything back trying your best to keep big transformers away from sensitive components. Do not stack one component on top of another. Do your best to route all the wires so they are at least a couple inches apart from each other, as well as being a couple inches from other components. Electromagnetic field strength declines as an inverse square function. So if you move from 1" to 2" that doubling of distance reduces the field strength to 1 over 2 squared or 1/4. So big improvement from even a small change.

Now the big one, elevators. For this time anything will do. The cardboard tube inside paper towel or toilet paper rolls is great, or paper cups- anything that can be fashioned to hold cables up and apart. Bonus points if you are able to incorporate rubber bands into this. If the cable rests on a rubber band so it bounces then it is isolated and that is what you want.

If you have a turntable pay special attention to where the phono leads come out. Route this cable so it has a stress-relief bend near the arm and is suspended on rubber bands. Because if this cable touches anything, anything at all, vibrations will travel right up the cable to the tone arm. Same thing happens at the phono stage end, but not nearly so critical here for obvious reasons.   

A lot of this probably sounds pretty goofy. I got a PM a week ago from a guy saying he read one of my posts like this and it was a lot of work but he tried it expecting maybe a tiny little improvement but he was writing to say Holy Cow this is amazing! So, like Nike used to say, Just Do It!

@millercarbon and @stereo5  That is some great advise. New here and learned something right away cool.

My stacks are typically amps on top, to dissipate as much heat as possible, then my pre-amp in the middle, then my disc player on the bottom. That keeps my inter-connect cables as short as possible.
If I have a set-up with an amp on the bottom, I'll invert that stack. Over the years I'm sure I've had every conceivable combination, not sure it makes any difference if your rack is solid. 

If you have a turntable pay special attention to where the phono leads come out. [...] Because if this cable touches anything, anything at all, vibrations will travel right up the cable to the tone arm.

+1 Good idea. I'm going to try this. Thanks.