HAVE CABLES EVER TAKEN YOUR SYSTEM FROM SOUNDING JUST OK TO SOUNDING GREAT? Experiences ?

I can't say that I have, but then again, I don't buy super-expensive cables, either. 

In my experience, the improvements, if any, were very subtle at best. But noticeable on my test tracks. Or I at least thought I heard a difference. But since I don't recall doing a blind A/B with previous cables I'm not 100% sure it wasn't me just "wanting" to hear a difference and thinking I did.

No, except speaker cables (Audience FrontRow on both systems). 

I found some gear are immune to RCA and XLR magic. 

On my headphone gear the cables made a massive difference. However, there was actual math behind the headphone cables from RAAL-Requisite.

@68pete rick makes great stuff. 

The best thing I ever did cable wise was make my own.

I've tried various gauges of cabling from heavy to light, various forms of wire- solid, stranded, ribbon, oval, square, rectangular, hollow, litzed, bonded, many strands of wire in their own dielectrics,  liquid, various types of wire- copper, silver, gold, tungsten, carbon, magnet wire, different alloys, etc. So when I made my own I combined some of these I used different types of high purity silver wire (no alloys) in solid, stranded, and ribbon form, all in different gauges, all individually in their own dielectrics. I used a heavy gauge for stranded (actually pulled from a shortened Cabledyne power cable), 18 awg for ribbon (Duelund), and a lighter gauge for solid.

They were a pain to make, and you need large connectors, but the sound was night and day over any other cable I've tried. If I could have found oval, square, rectangular, or hollow wire (though I know round, oval, square, and rectangular wire can come in hollow form) in silver I would have used them as well to get the full gamut of the experience, but you'd need to special order those in large quantities and finding any secondhand can be a pain (I know some Cabledyne cabling used rectangular silver wire, Analysis Plus mentions that their hollow oval silver wire has a copper strand in them, not sure if this is just a single copper wire running through that can be removed or not).

I know Clarus uses a similar ideology for making cabling, but I haven't tried theirs to compare them to mine, I'm just glad that I'm in good company.