Thinking about getting an upgrade of my Amex to Platinum, primarily for the 15,000 miles. Up to now, I've found good ways to grab miles for free, but I think to get to my target level I'll have to pay the $150.

I got an offer in the mail, seems to be the same as this:

http://www304.americanexpress.com/ge...Delta-Skymiles

Some of the rules here (but not all):

https://www304.americanexpress.com/p...-card/PA-36182

Two questions I'd appreciate help with:

1. Can I cancel/downgrade at any time and retain the miles I got from the upgrade? (The rules say I pay prorated amount to get me to December - if I can pay for just a few months and get all 15,000 miles, then cancel in December, that's obviously cheaper)
2. My mailing says the upgrade isn't available to existing Delta Amex cardmembers. I have one regular no-fee Delta Amex card and another that is unrelated to Delta. Will I be excluded?

I can call and ask on question #2, so I'm most interested in the first question.

Thanks!!!!