now that you are interested, i want to share the situ here a lot more. in the west, coin collectors maybe far more than note collectors, but in China note collectors are contrarialy much popular, some of the reason maybe in the US or EU, the note design is just person on it for toooo long( one century? i am not much familar with West notes), the Chinese notes got so many elements and designs in different times and of course it got huge populations, people are attached to these colors or designs on old notes used in their daily past.
PMG has until now graded 500M banknotes, about half or more are Chinese notes..... here people grades PMG banknotes not in pieces, but in stacks or in bundles..........
So about your question, people here mainly collect domestic notes, of which they are attched to. but little by little in big cities, US dollars with fancy numbers also got premium now.
here we have birthday note/ marriage note/ leopard note(111/222/....)/ lion note(1111/2222/....) /tiger note(11111/22222....)/elephant note /dragon note/ Sky note.....
and always bear in mind, numbers got 4(death) and 7(persetic) in it can discount 50%~70% from numbers without them....
people prefer numbers with 6(good luck) and 8(good fortune). hahahahahahahahahahahah