I think I may have found a work-around, but it's going to take 48 hours to confirm.
Don't ask. :)
Why, either I got really drunk and lost two days, which doesn't seem likely as I'm still wearing matching socks, or that was the fastest MySpace has ever responded.
Okay, this is how you re-use an e-mail account you've already used to create an App. First, sign-in to that App's profile, using the e-mail and password you provided to create it. It doesn't matter if you've deleted the App already, the profile still exists (which is why you can't re-use the address). Go to Accounts, and go through the process of Cancelling and Removing the account. It's a bit of back and forth with e-mails and lots of confirmations, but once it's through, your App's profile will be completed deleted (and finally removed from your Friends list - if you haven't noticed, deleted Apps still hang out there, trying to be cool, hanging out with the other, non-rejected Apps).
MySpace may take up to 48 hours to completely delete the account from their records (though, it only took about six hours for me). After that, you can use that e-mail address to create a new Application.
Given my spelling, maybe I did get drunk for two days...