I'm back home now (in Skurup, Sweden), safe and sound with all my family
Didn't get to see much of Hamburg, unfortunately - After running around like manic rats to solve our more immediate problems (like, somewhere to sleep, reservations for the next day and something to eat), we were all completely knackered and just slept
Still, Hamburg seemed nice enough in the few things we saw on the way, so I'll save your recommendations for the next time we (hopefully in a more planned way) drop by. It is, after all, not more than 8-10 hours by train, on a good DB day