Originally Answered: Can you put a backup file of an iPod Touch onto a different iPod Touch?
A) your iPod life-span theory applies to hard drive devices, not flash memory. B) In spite of A, you do need to be concerned with backing up your content in addition to the iPod backup feature in iTunes. C) You should be backing it up now. You should have been backing it up all along regardless of future iPods.
While it's great to be able to download directly to the device, it's more complicated to then transfer that content to the computer than it is to download to the computer in the first place. Even in the case of downloading to the computer then syncing the iPod, you need at least one ADDITIONAL copy of any and every file that you don't want to lose, especially those that you paid for. Obviously, the time to institute a back up plan is before you need it. If you have back up copies, syncing and organizing content on a new or additional iPod is going to be quite simple. I wouldn't count on that being the case if you're going to do it from the backup/sync info, as you call it. That's great for iTunes purchases, but not so much for the other content such as contacts, photos, notes, home videos or even songs imported from CDs or from other online sellers.
So, there's not really a "yes" or "no" answer to your question. My best advice is to get serious about other back up and worry about your iPod dying when the time comes. And, FYI: with a free Hotmail account, you get 25GB free online storage from Sky Drive. Off-site is the safest method for back up. Uploading can be time consuming and each file can't be more than 50MB, but it's perfect for song files; and, you can't beat free.