The 1/20th 2004, only 9,880 were minted which is the second lowest mintage (lowest is 3,890 in 2003). Could fetch up to $100 on
ebay.
Why is the 400th anniversary proof set worth less then the 2005 one? While there were fewer sets sold in 2004 than in 2005, I believe that the demand for the first selective gold plated silver dollar partly explains the price difference. The 2005 selective gold plated coin was only available in the Proof set, while the 2004 Proof silver dollar was also available individually. In 2004, die hard silver Dollar collectors did not have to purchase the entire set just to get the dollar. That changed in 2005 when the Mint decided to issue "unique" proof dollars to spur demand for the Proof set.
The other aspect, less obvious is that the Canadian flag may have more significance. But I don't know for sure.
In total, there were 106,974 2004 Silver dollars minted, Vs 63,562 for the 2005 selective gold plated.
Whats NCLT: Non Circulating Legal Tender. "By definition a Non-Circulating Legal Tender coin is a coin that has been issued by a recognized monetary issuing authority, but is not intended for circulation as a medium of exchange." -http://www.blackmountaincoins.com