No idea on “cheap Chinese cables on ebay” but there’s always Monoprice and whatever generic or otherwise mfgrs you can find on Amazon (they usually have discounted prices on “name brand” like Belkin and Hosa as well as various unknown brands). As far as cables making a difference, this is IME so take that for whatever it’s worth. I think the potential is there, primarily WRT build quality and shielding. This doesn’t have to mean crazy expensive cables, but there are plenty of unshielded RCAs with really dinky connectors out there (and some shielded RCAs with dinky connectors too) – going up to something that’s better put together can solve those problems. As far as this imparting any benefit to the music – I honestly can’t say. I own some relatively expensive (still in that sub-$100 category but more $$$ than pack-ins or whatnot), and have tried some genuinely expensive ($100s/meter) cables, and would say IF there is a difference, it is extremely subtle. I think this is very much a “past the point of diminishing returns” consideration.
As far as what brands I would suggest, I’ve never had problems with RadioShack’s “premium” or “gold line” (or whatever it’s called these days) stuff, Belkin, Hosa, Grado Labs, or AudioQuest. I’ve had few problems with Monster (and never signal problems) and many generic brands. I’ve had very mixed success with Monoprice – their standard/basic cables have never given me an issue, but their “premium” cables have had a near 100% failure rate over time, all because the connectors they use are not awesome. 
On metals and such:
Pure copper will oxidize, so if you have a pure copper cable you want to make sure the jacket/etc is well put together. This is more commonly a concern with speaker cables but it’s something to think about regardless. Gold plating is used to prevent this, but it isn’t the only way to address that issue. Nickel plating is also used on many connectors. I honestly can’t say if there’s a difference in terms of longevity, but I have relatively old (at least 10 years) cables as examples of each that are still working properly.
I can’t imagine that anyone is making pure gold cables (the cost would be unbelievable); I’ve read about “solid silver” cables but never seen one in person (I have tried cables with silver plating and I’m not sure it made any difference – it looks pretty though) – I know silver can also oxidize.
Finally something to keep in mind: whether or not you end up liking cables as another component class for your system, realize there are *tons* of fakes out there. Especially for more popular brands like Kimber, Monster, and AudioQuest. I’ve seen fake Monster cables over the years and the quality is usually abysmal; Kimber and AQ claim similar things about fakes they have observed of their own products too. If you end up wanting to go with a premium cable like that, I would strongly suggest figuring out who is the proper dealer for whatever brand you want to try, and going that route.