Can hi-end cables benefit less expensive electronics?

I've used inexpensive DH Labs cables in my office system (Cambridge integrated amp and NAD cd player).  Never tried anything better, but I doubt it would make much difference.  Speakers are decent Wharfedale and a NHT subwoofer.

What I wonder about is my older systems.  Adcom GFA-555 amp, NAD 1300 preamp, and Vandersteen 2C speakers.  Back in the day, Monster was the good stuff.  In hindsight, I wonder how well a system like this might have performed using good cables... 

Great question. Of course there is no absolute without trying. But here goes.

I actually bought a transparent cable and put it on inexpenive components long ago. It sounded terrible. But that was because I had a very noisy fatiguing solid state system with very revealing speakers. Cardas golden (reference) speaker cables warmed things up and sounded much better. I put the transparent in the closet.

Twenty years later I had good quality components and those same Transparent cables sounded fantastic. So, it is a mater of what the sound of your components. Transparent will get the most out of them if good. I use Transparent throughout. Looking at your system my guess is that the Transparent would be a great investment and net you better sound now and in the future.

That’s my guess.

BTW, I have no idea why but speaker cables, interconnects, and power cords of the same manufacturer and level tend to do exactly the same same thing for the system. I find this strange, but it has been true for me all the time

Is a high-end digital cable in some cases able to make it a worthwhile investment in a setup which is not top hi-end?

A good digital cable is critical and worth exploring and investing in, but how much to invest is very system/budget dependent.  In my system a better digital cable made a very significant improvement and regretted waiting so long to upgrade, so with your current DIY cable I’d certainly encourage you to try something else.  And getting a better digital cable will obviously also pay dividends if/when you upgrade other components, so there’s that.  Why are you locked into the Transparent cable that may or may not work best for your system/tastes?  Whatever you do, and as with all cables, I’d make sure you can try the cable first so either use a dealer who will let you do that or buy used.  Just my $0.02 FWIW, and best of luck.

I locked into Transparent on the basis of reviews (!) and the fact that I can get it at nearly half the price ;-) Also I bought much of what I own based on intuition and somehow I feel that this cable may appeal to me... ;-) Foolish, I know... ;-) But in my case, it's not whether it's the best cable for me, it's a question of whether I will like it without listening to anything else, for which I would have to pay the full price for ;-) Crazy, I know... 

And just to remind you, I’m currently using a Furutech FX - Alpha Ag + CF-102 NCF R. By the way, I’m so surprised I’m getting such great answers without the crowd saying that cables don’t matter. What are they doing? Barbecue?? :-)