I know in the past a down grade from an AA to a bronze card kept the open date on the original card. I am in the process of converting (again) that same bronze card to a Forward.

In my view the benefits are as follows:
1. keep original date/history for average age.
2. Doesn't waste an app.
3. If you are in the AOR game eventually you will max out the cards with an issuer (and then you will have to close to open, spend more time with reconsideration). If you need to keep one card in a slot for aging purposes, then ideally it would be a good earner with minimal sign-on like Citi Forward or Chase Freedom.

My 45 days should be up and I'll get my new card in the next week or so. Then I'll wait a month and pull a free credit report. I don't think Karma or Sesame will show it cleanly and I am too cheap to pay to monitor.