You said, "you then can re-pitch the mss you sent during the poor economy."
Can I do that? I thought once an agent/editor rejects you it's over.
First, let's clarify something. An agent/editor is not rejecting YOU. They are rejecting your manuscript.
That distinction may not help your heart in the moment that you're reading the form letter, but once you're through crying about it and you're ready for rational thought, it's an important distinction to make.
Unless they've specifically said that they never want another word you've written to cross their desk, you are free to continue to send new queries to the same agents/editors who've rejected previous ones.
Okay, now for the issue of re-pitching previously rejected manuscripts to the same agent/editor. In most cases, your previously rejected queries/mss will have been rejected based on the quality of the work, so no, don't waste your time re-pitching old stories. Move forward with what you've learned since you submitted that first mss, and write new stories to bring to the table.
However, if you know for sure that your mss was rejected solely due to marketing reasons, such as a slow economy or timely issues, you might (that's MIGHT) be able to re-pitch at a later date if: 1) those marketing reasons have changed, and 2) you are now a published author through the agent/editor who previously rejected the work.
For example, let's say you submitted a vampire book pre-Stephenie Meyer and it was rejected because vampire books weren't selling. However, the next novel you submitted was accepted and published and sold at or above expected levels. Then Meyer bursts onto the scene. It would be perfectly legit for you to contact your agent/editor and remind them that you had a vampire novel they'd previously rejected because vampires weren't selling but now that they are selling, would they like to take another look at it. (Except you'll be much more eloquent in the wording of your query than I just was.) (And yes, it would be a revised query that you would send them, with a reminder of your basic plot, how it's like and unlike Meyer's book, blah, blah, blah.)
A future scenario might be you've just received a rejection and it says, "Loved the story. Wish we could publish it but must reject due to the current economy..." Then suddenly this fall, Obama saves the world and we're all sitting pretty with gobs of cash to burn. In that case, yes, you could send a quick 1-page query to the agent/editor and say, "When you rejected my manuscript, The Story of Edgar Bookman, last winter, you said that you wished you 'could publish it but must reject due to the current economy.' Now that you have plenty of money, would you like to take another look at it? " Then continue with the basic query to remind them of what it was.
It could happen. Maybe. But ONLY if they indicated that it was solely economic reasons that you were rejected.
However, outside those two scenarios, no, re-pitching old stories is not a good idea, unless your agent/editor specifically asks you if you have a book dealing with a certain topic, and then you could say, "Yes, but you rejected it two years ago..." and go from there.