There is this saying in China, "". In my broken English it means, the quality of proof is not as good as expected for a proof, and the quality of BU is much better than what is expected for BU.
I am not sure about silver/gold proof as I don't have any. I do read about the complain people had about the quality of proof coins. They are expecting a better job from China Mint.
For modern China circulation coins, other than silver/gold, most collectors (unsure about investors) do not chase for proof coins. For example the Fen coins collector. They consider the difference between the proof and BU is about the minting technology, and not design difference.
For Fen coins collector, they do not include the proof Fen in the complete year set of 1955 - 2011. It will be impossible for many collectors to complete the set if proof coin is included. There were only 660 set of 1986 proof ever minted (and btw, this number is undisputed, and the market value for this set is at least USD 20,000.00, if you happen to see one for sale. Oh! That is so much better than the pagoda! )
1992 proof and BU set is selling at almost the same price. My opinion is, get the 1992 proof.
For other proof (I mean other than silver/proof), they are gaining recognition at slow pace, are hard to find outside of China, and perhaps it is good if you can get hold of them.
There are a few dedicated collectors in China into educating collectors about proof coins, but don't expect things to change overnight. It may be a long journey.
Just so I don't confuse everyone, I have no interest in silver/gold coins, and my comment is about the non silver, non gold, non medal, modern China circulation coins, which has quite a huge collector base as I know.