Never been Brook so can't offer suggestions, but I agree about the collecting scene there being vibrant - seen lots of collectors from there posting on fora. Some nice get together shots too, with the same focus on Rolex you mention.

Lots of shops close together is good news - it's one of the things that lets Berlin down a bit compared to, say, Munich - the worthwhile shops are spread from one end of the city to the other. Maybe try taking a nice, ripe (and stinky) durian in when haggling, might get you a cheaper price just to get you out of the shop!

It's quite an important market for TAG Heuer, they have produced a number of special watches for the region, with distinctive bluey-green highlights. That's relatively recent though, with Singapore's rise as one of the Tigers, I doubt it was quite as important in the Heuer days. City reports are always fun though, let us know how you got on!