I vote none of the above. By lumping all tweaks together you are at great risk of having this whole thing seen as arbitrary and illogical and with a high likelihood of backfiring.
If I refine the alignment of my phono cartridge, I'm tweaking it. If I clean my plugs and jacks, ditto.
Definition of terms? You can't lump all tweaks together and make any kind of meaningful statement.
That said, I doubt if you could prove something like tuning fuses can't possibly work. I'm not an advocate of tuning fuses, but likelihood is not proof.
It will be interesting to see what's written here.
neo
Neo makes some good points here, so I will experiment with tweaking my post.

I wo
No, that's exactly what tweak means.
http://www.merriam-webster.com/dictionary/tweak
neo
I agree with Doc that cleaning contacts, adjusting turntables are normal maintenance. These practices actually fit the Webster definition better than the current use of the word which I take to mean buying something based on the claims of others that cannot be supported in any other way than subjective.
I would like to see members here sharing things they have done to improve their systems, especially things that do not require significant expenditures of money.
As to tuning fuses, unlike magic dots they can be harmful to your system. The manufacturer is making a claim that he reduces microphonics in his fuse construction. Just how is a fuse microphonic and just how could that affect my system even if it was? I think I will go hook up a microphone to the power line and start talking to people thorough their systems. Gee why didn't Bell think or that.
One of the many things that offend me about the purveyor of Tuning Fuses is his claim, as expressed on his website, that manufacturers use the cheapest components they can find.
For example: est. 90% used IC's in the Hifi - Equipment cost around $ 0,80 a piece, but the Highest - Quality IC's cost est. $ 60.00 a piece or more! Perhaps he naively believes that price equals quality. Perhaps he doesn't know or care to find out that a $60 op amp (there are very few) is designed to optimize some difficult characteristic, like offset, that wouldn't matter a hoot in an audio application. Perhaps he doesn't know that some op amps are very expensive because they are obsolete and in short supply. Perhaps he doesn't know that some 60 cent opamps are also available in a metal can and because that configuration is made in very small quantities it costs a lot more.
When I go shopping for op amps, such as the one I am using in the servo for my OTL, I note that the same part number varies in price widely with the letters on the end. Perhaps he doesn't know what these letters mean. In many cases they mean an op amp is selected from production to have optimum characteristics in some particular area that might be important in one application but not in my application. The letters also describe the temperature range the part is guaranteed to operate over. It costs more to make or select an op amp to run over a wide temperature range. We don't need our op amps to operate from -55 to +125 C. Here are the temp ranges used by makers of electronic parts. Wider ranges cost more. Is that money well spent or would it be better spent on a bigger power supply or more isolation from the power line.
http://en.wikipedia.org/wiki/Operating_temperatureThe silicon used in a $60 op amp is the same silicon as in a 60 cent op amp. I invite you to read the whole page
http://www.hifi-tuning.com/index_eng.html. I also find it odd that although he is the creator of HI FI Tuning Fuses I could find no mention of them on his website.
Speaking of Mapleshade, I have been getting his catalog for years and I feel the man is making an honest effort to make something real. At least his products won't damage your system. His brass tube covers have a good chance of reducing microphonics in tubes. If properly used they do no harm. I do think it is appropriate for us to mention particular problems we might have encountered with anyone's products. For instance I repaired some of his cables and found the copper foil to be very fragile. That is something that would be useful to know and perhaps he could improve.
I think we all want to see better products. I think the ones making specious claims should be discussed as to the validity of those claims. My interest is education. Read the post
http://www.audiocircle.com/index.php?. I entered this discussion to give the reader some simple rules that would allow him, from reading simple specs, to determine if an amp has the possibility of being class A. Many manufacturers are claiming class A when their very specs say otherwise. Once a person understands what class A means he can decide for himself is the claim is true. The discussion has also brought up the question
Is class A bias even necessary in today's amplifiers?I have chosen Tuning Fuses as an example because the claims by the maker and the reviewers are so much like what Harry P said to me years ago about High End audio. "Hi Fi is a drug and I am the Hi Fi pusher" When a reviewer of some merit says "I loved listening to this CD player, but when I replaced the fuse this rather good player became a world class player" I have to wonder what is going on in his mind. We who make things work hard at our craft. OEM pricing on many "audiophile" capacitors, fuses etc. often has a 70% discount off what the public can buy it for. If the maker of the CD player could transform his good player into a world class player with a fuse that cost him a few bucks, wouldn't he.
High End audio is not supervised or regulated by any agency. Consumer Reports doesn't even notice us. Perhaps we need some organization or forum to look at equipment objectively. We certainly have enough organizations looking at it subjectively. Although subjective tests may be amusing there is no end to them.