Will The Lincoln Commemorative Cents Be Key Dates Someday?

Recently, I just bought a 2009 Proof Set locally for around $20. The guys bought like 10 sets or so when it was released and I guess he sold this set because the 4 Proof Cents turning reddish color. I know many collectors don't like toned Proof coin (ie: prefer original color); I, on the other hand, love toned coins so I didn't mind.

I know people have discussed on here before regarding those toning, but it seemed like no one have completely answer the question: Why did those Proof Cent turn color (only to reddish, so far)? What can one do to prevent it or stop the progression? Lastly, personally, how will such toning affecting the coins' value? Also, does the similar issue happened to the Satin Finish Copper Cent, I haven't encountered such issue?

May be I should create separate posting or would someone redirect us to any existing post.

Thank you all.