Hi, Prethen!
I have always felt the 3CNs have been undervalued. The design is beautiful IMO and a 3 Cent denomination is a really cool/unusual coin to own. The proofs and business strikes are very scarce, and priced extremely low when you factor in age and mintage quantities.
Really it comes down to the demand just not being there. I have a couple of theories as to why that is.
1: The 3 Cent denomination, because it's unusual, tends to be overlooked.
2: Because so many years have such few mintage quantities, completing an entire set is a daunting task. I remember trying to buy the 1885 (business strike) as an investment piece. After scouring the earth for a month I could not find ONE! I'm willing to bet if, say, only two or three years of the 3CN were scarce the 1885 would be worth triple its current market value.
A tip of the hat to any of you who have completed the entire 3CN series!