Just an update: I got off the underground at Feldstraße and that part of town is just 100% cool. The fleemarket is awesome for anyone who's visiting Hamburg, they have loads of cool retro crap eg 50s radios, 60s ball clocks, dial telephones as well as ghetto blasters n other cool stuff. Sadly I have to get home on the train so I didn't buy anything there. But round Marketstr. where Fishkopp records is there's a ton of cool alternative stores and another record store with some cool stuff.
Fishkopp records seems to have really lazy owners as they still weren't open when I got there, so I'll check it out again next week along with Burnout records (couldn't find it). And there's a giant bunker which makes the part of town even more cool.
But I have to say I'm really impressed with Hamburg and the bit around Feldstraße has the alternative/bohemiam thing going on without being some tacky tourist trap that Camden Town and Kreutzburg (to lesser extent) are becoming. And the wall art around there is better than that in Camden and Kreutzburg.