There might be dubious value to actually keeping that first AMEX for its credit history. I've found that every AMEX card I've opened since I got my first one (except business) has been assigned the Opened date of my first AMEX in 2009. In other words, if you open another AMEX and correctly enter a card number you already have where it asks you - you should get a opened since date of whenever you got your first card with them, and it's basically like doing a product switch since you still have that account age on your report.

I'm in the funny situation where the more AMEX accounts I've opened, the more my credit score has gone up as each card I have been getting has been adding to the average age of my accounts.