Most useful tweaks that are sensible and really make a noticeable improvement

Mat+fo.Q+TC

Don't say I didn't tell you.

Although the last few posts have been humorous and entertaining they really are outside the useful part of the original posts.
Please try to stay with the intent of the OP which is useful improvement. 
Geoffkait has identified some potential useful tweaks it's up to the reader to accept or not them to be valid. I for one appreciate geoffkait's input to the discussion.  The one I will try is the contact enhancer as it is logical and already used in some form in automotive applications, i.e dielectric grease as a moisture barrier. 
Let's put some real and tried useful tweaks out there for the readers and who knows you might be a star audiophile. When I get some of the contact enhancer I will post my results for sure either debunking or endorsing Geoff assertion.

Although my previous comment was in jest, it does, in its own way, contribute to the discussion...by hinting, as useful information, that Geoff's recommendation about freezing electronic components and accessories is, in my opinion, a joke.  Geoff will, as with his other ridiculous tweaks (like the green magic marker on CDs tweak), want you think he believes in most of this BS....but I'm thinking he is really smarter than that.

Even if some of this stuff had the ability to somehow (refuting science) modify, hopefully in a positive way, the sounds coming forth from your speakers, they would be so subtle and to defy aural detection.  And I'm not referring to the OP's "tweaks" mentioned in the original post.  Those can and do actually make a difference.

Wow! I don’t think I’ve ever seen anyone gets his panties in such a twist over some audiophile tweaks. Slow day at Subway, I suspect.

There is a blurry line between "willing to experiment" and "being gullible".

It would be less than useful if contributors only stated what is "useful". Adding their opinion about what they perceive as some kind of a practical joke has certain value, too.