With the W series, the walkman is the most important thing in there. Explains the W doesn't it :). The W series also gives you more extra stuff like a headset and a memory stick. You don't get that with the K series. And if something comes with it, it won't be the same quality as from the W series.

You say you don't really need the walkman and the camera is not that important, then you should just look at the price :)
I like the k530i and the upcoming W890i. Especially the W890i. don't know about the price though.

Just go to your local cell phone dealer and have a look around. If you have any questions, feel free to ask :)