In the long run, I don't think that the preview will have any effect on the value of TWD 61. Savage Dragon #102, the Masters of the Universe book, and isn't there another one with the Invincible #1 preview??? None of those have any value.
With that being said, I'm hoping it will have some added value because of the insert in the short term because I've got a copy up on ebay for $12.99. I bought 4 extra copies of #61 because there's a new character and it's the first issue after a trade. #49 was tough to find, #55 is not.