Don't "kill" sponsored posts (allow to be showed again with show all posts).
Sponsored posts are quite targeted and useful (at least to me & till today;) but once are read they are missing and show all posts doesn't show them any more.
I think will be no harm if they are treated same as posts (or keep them in a special folder for future reference)
You can now see an archive of our Sponsored Posts here:
You can get to it from a link titled “Sponsored Posts” in the drop down when you hover over your user name in the upper right hand corner of the site.