Anyone else have jars full of Queen's-head coins? Do collectors pay a premium now for them?
(The money change shops in North Point etc are reliable. No problem changing foreign currency there or vice versa. Just check around a bit first since rates can vary slightly.)
No, pre-1993 coins are extremely common outside HK (at least in Europe), they are still about 50/50 with bauhinia coins for some reason. Given that they need to be brought to HK before they can be used, they can only be sold at a discount. Inside HK you still get QE2 coins in change every so often (I only used cash a handful of times this year but I still got one) so I doubt anyone would pay much more.
The only coins that really go at a premium would be King George VI or earlier, or coins that have never been touched and perhaps professionally graded. Also the 1997 series with special designs. 5 cents and the bigger old coins as well as the decagonal $5 might go for a bit more but it's hardly worth it for the time you need to spend sorting them, unless you enjoy that.
Best walk-up exchange rates appear to be with Little Girl in Sheung Wan and Capital Exchange in Central (rates on Facebook) and TST, you can do better elsewhere if you book in advance via whatsapp (in Chinese) but unless you are changing 6 figures the difference could be less than the transport fare.