too easy to exploit the system and "double-reward" yourself by reposting your old work.

As a new user I do not see this as an issue. It would only be a double-reward if you upvoted yourself on the old post and then upvoted yourself on the new post. That is the only way an Author can "Double-Reward" themselves. If I saw an Author post 4 months ago, and then the same post today, and I remembered that post, then is it not for me to decide if I want to reward the post again? I mean face it 4 months ago my vote was worthless, $0.001 if that. Today at full power it is $0.070, I now have the chance to give a semi-Real Reward to them. Why should steemit be different than any other type of publishing company. If you were to go into any music store or any place that sells music I am sure you can buy a copy of Elton John's "Goodbye Yellow Brick Road" Album. If you went into a bookstore I am sure you can buy a new copy of Anne McCaffrey's Dragon Riders of Pern. Why should I view steemit differently. The reason you can still buy those items is marketing to a new audience. I hope that steemit continues to get new audience members.

So in conclusion I myself do not see reposting information from the past as a bad thing.