cables are they worth it?

A good quality van den hul cable, as Jaybo suggested, should last much longer than a walmart cable. In a humid environment (Netherlands?), cheap cables will corrode more quickly (discoloration of the copper under the jacket) and with many cheap cables the jacket becomes stiff and may eventually develop cracks irrespective of humidity. These are good reasons to get a better cable and only you can decide if this is enough to offset their higher cost. Like a good quality car a good cable may be more expensive but can be expected to last longer with lower maintenance/running cost. Just two cents.

If you're considering to take the plunge (for this purpose I will presume you'll upgrade to the Symphonic Line or something similar as a new amp), don't do it half-heartedly.
Having said that, $200 for an IC (or should that be EUR?) will certainly buy you good stuff, however, whether it will better your Cardas is for you to find out. Since you're in the Netherlands look up the Tweedehands section on www.hifi.nl where you will regularly find a number of Siltechs, among others, on offer (e.g. right now there is a SQ28 G3 interconnect for EUR 150).
$50 for a powercord on the other hand won't bring you anything, just wasted money. Kemp powercords have been offered on hifi.nl starting from EUR 70 and that is, imho, really the minimum you should be willing to look at in that respect.
For second hand also look up www.audiomarkt.de and then of course there is the Gon, but if Dutch customs are as greedy as German don't forget to add 24% duties on sales price + shipping cost to your total expenditure.
And by all means stay faaaaaaaar (can't possibly get enough a's in there) away from ebay.
For buying new, a well kept secret and overachiever when it comes to powercords is High-End Netzkabel by Kalle Miltzow (between EUR 70 and EUR 250)
http://shop.strato.de/epages/61385824.sf/de_AT/?ObjectPath=/Shops/61385824

Btw the Synergistic Research Tricon Analog is indeed the best phono cable I know but I agee it looks a mite out of proportion...

Cables can make a difference. Or should I say cable types. I'm running Kimber Hero's through out my system. I had a pair that I was going to use from the tt to the pre..... Well, that didn't work. Very bad hum. So, I put the cheapo cable back on until I find a fully shielded cable. So now I'm running the Kimber from my $20.00 ebay find NAD FM tuner...... The cable cost 5 times the tuner..... go figure...

If you have the possiblity of spending thousands on cables, don't do it! Upgrade you preamp and amp, that will do far more for your sound than a cable upgrade.