It all depends how crazy you want to go; you'll be very surprised to see how much some people spent for only a very small gain. And most think it's worth it!
Audio is not a product, but a process; there is no definitive "ultimate" setup. A lot of people are very happy with MP3 on an iPod and a boom box; some others are spending $90k on a pair of speakers and they keep changing stuff because it still doesn't sound "right" to them.
This is the reason why we see cables selling for tens of thousands and things like the Blackbody ambient field conditioner, that goes for $1300. It will eliminate "near field electromagnetic (EM) interaction" between all your devices and improve sound quality; that's what the manufacturer says.
The secret is to know where to stop, and to trust your ears more than any review. I'm not saying reviews are not good, but in the end you are the "judge, jury and executioner" and it's your money to spend.
In any case, if you've got even a fraction more knowledge then what you knew yesterday... it's all that matters.
