Upgrade path the same for cables ?

Aside from system matching, really good cable will sound good in any system. Also, some cables are very overpriced and some not. But very best cables are always expensive and they should be. I believe, it is just as difficult to design and build great cable as it is with components.
In my modest system DiMarzio interconnect is overall almost as good as Purist Audio at less than 20% the cost. In any case, when it comes to upgrades, cables or components, I advocate rare but big steps approach not often and small. And of course you spend more doing it, usually at least a double for used pieces.

Currently have :

Magnepan 2.7 qr's
Wyred 4 Sound st-500 mono
Lector Zoe Preamp
PS Audio phono pre
Technics sl-1200 w/ at 150 mlx
Acoustic Research IC's
Morrow Audio sp-3
Room treatments ( panels )

Would like to get more detail to come out.

Mr B- Try the Synergistic Tesla line(especially the Apex & Tricon Analog). Both will allow you to hear exactly what is going on upstream(for better or worse). The Kimber Select line(1030's/1130's) are also excellent, in that regard. I own some of both. Good cables WILL NOT sound good, in ALL systems. ie: If your source components are grainy, bright, etc.; you MAY be happier with a less transparent cable. Not the ideal way to correct system defects, but- many use cabling as tone controls. When some experience sounds that don't appeal to them(ie: upstream defects exposed by a good/transparent cable), they blame the wire. An excellent/transparent speaker cable= Analysis Plus Big Silver Oval(my latest upgrade and less expensive than what I was using).

i will recommend you to try Yamamura cables....no longer made, but you can sometimes see them here used. I use these cables as my reference for many years now and did not found any better yet....My friend has also Maggies and he also uses Yamamura cables with them.

But very best cables are always expensive and they should be.I believe, it is just as difficult to design and build great cable as it is with components?

I added the question mark after this statement because all cabling comes off of spools.With no or very little change in it's structure. The only thing that's added after is an RCA plug or spade or what ever termination is added to the finished product. I find it amazing that anyone would pay for such a common product that has gone through very little structual change.