Since you were there anyway, why didn't you trade in Infamous 1 and 2 for Infamous Collection in the same transaction (or if you prefer Best Buy credit, Infamous 1 to BBY and Infamous 2 to Gamestop)? Infamous 2 TIV held at $9 today, Infamous 1 might still be $4, so that's $19.50 after bonus at least.
I'm a collector. I NEVER trade in games. I would buy a redundant collector's edition before I even considered trading in a game I already own.
For reference, I already own all three of the Ratchet and Clank games for the PS2, yet I still purchased the Ratchet and Clank collection. And I'm going to keep all of them. For me, it's not just about always having one playable copy. I like having an original copy, as well as a high-res playable version.
The same is true for the Infamous games. I got those titles brand-new for really good prices. They are the original copies of the games complete with boxes, instruction manuals, and inserts. On top of all that, Infamous is a really good series. I'm never trading those.