Agreed, GDG, pretty scarce coins, the higher- graded 2001-D. I like them, they are some of my favorites. But it's pretty well-known as scare and its pretty expensive, so I don't consider it a "Sleeper". But the recognition of the "Low D" and "High D" varieties may make it a "Sleeper" soon.
The 2001 have been the lowest priced of the early 2000 coins, and the 1/2 especially underappreciated and undervalued..until now. They lagged the 2000, 2002, and 2003 by quite a bit in price until just recently despite similar numbers of 69s.
But there is at least one gold panda I have seen which is so far a lot scarcer, and surprisingly off the radar completely, and low priced. Overlooked and undergraded and underappreciated, and maybe it'll stay that way for a while.
PandaCollector's new book may mention it.
I look forward to owning his new book.