Non-silver proof and mint sets are collectibles not investment items as most, if not all, of them decrease in price over times
Here is an example using Pres. dollars. Mint cost followed by current retail price. Of course you could find someone to pay more than retail but it is just for a reference}
2007-S Presidential Dollars $14.95 $6.50
2008-S Presidential Dollars $14.95 $11.00
2009-S Presidential Dollars $14.95 $8.50
2010-S Presidential Dollars $15.95 $14.50
2011-S Presidential Dollars $19.95 $20.00