Looked at doing the K04 upgrade and it just came to too much dosh to do it the right way, easier to sell your car standard and go up a grand or 2 and get an ED30 or similar and then spend the other 1k on suspension and towards a chip. It needs new turbo (obviously), new cam and followers with a new upgraded fuel pump... that was were I lost track of what I was told. Cool if you can do all the work yourself I suppose but hand it to a trusted specialised and you don't get much change from 3k if your lucky.
Saw a brand new K04 turbo go on ebay for about 750 and thought it was the time to act until I got the estimate on the other work - then calculated how much less my car would be worth after the work, not being a true ED30. Hard to sell a half thing unless you go for the full retard and upgrade everything and sell it as a fully sorted car - even then it's not a good marketplace at the moment for getting rid of these cars.
I would still do the job though if I decided to keep the car for track days and fun and didn't care about selling it but until then it will be a rip-snoarter K03, lets face it your only losing out on about 40hp in real world high tune. Throw in a Milltek full, filter and a stage 2 chip and you gt 260-270 anyhow, some get 300 if you push the boat out and with the ED30 you will get a similar increase 290 - 340 if u push the boat out.
Love your K03 and cherish it, it's what you were blessed with.