Yep,I have tried a few.From green pens to Dummy plugs for the inputs I wasn't using.
Probably the best ,as you have found out ,is connection enhancers.I use to use one that,from memory,was called "Kontak".Came in two parts and stank.It did improve the sound across the sheet, if you ask me.Cleaner(no pun)and better presence.If that makes sense.
Green pens;not much diff,perhaps better spatially.
Rain-x;Not too much diff.
Dampening materials;Pretty good.Improvement in lots of places across the band.
Shorting plugs;Not much diff.
Magnetic donuts for cable RF rejection;Good if your cables aren't so good.Same thing for wrapping you cables in foil.
Spikes;Great tweak for most gear.Thicker the better but athletic spikes are better than nothing.Short ones.
Blu-tak;Here there and everywhere.Not to bad.Stuff from a car place is better.
Internal re-wiring of speakers;Very good tweak.Don't hold me responsible for your own inept screw ups with a hot iron.Disconnect from your amp,of course,prior to sticking the hot stick near them.Remember speakers work on electrical/magnetic principles.Some Mags are very strong indeed.I do not recommend you try this,if you are not sure.Will void any warrenty still applicable.
Cleaning mains plugs and "kontak"ing;very good.Not the bits in the wall,though.Leave the wall sockets alone.Pluging-in and un-plugging lots of times may help clean the wall sockets a bit before finally kontaking.
Bits of foam cups cut and placed around tweeters;some diff.Use blu-tak so it can be removed.Felt around tweeters same deal.
Heaps of other things.Some work well.Depends on the listener and the gear,of course.
Have fun with it but avoid things that are hard to reverse or dangerous.Like installing your own dedicated mains spur.Less your a sparky.
