You need to keep the Explorer card open for at least one year if you plan on doing a product change to the Club Card (you won't receive any sign-up bonuses on the Club Card for going this route though).

There is no mileage bonus for the Club card, only a $95 statement credit or in some promotional circles there's an offer for your first year free, a $395.00 value.

Did you know that you can have both an Explorer Card and a Club card? If your credit and income qualify, you can get both now and then cancel the Explorer Card when the annual fee comes due.