If you have good use for your AAdvantage card, that's one thing. But you don't need an AAdvantage credit card to prevent your miles from expiring: If you redeem miles for a flight award (some can run as low as 5,000 miles) that redemption will extend your mileage-expiration date. And if you were to subsequently cancel that award before the departure date, your miles and cash paid would be refunded at no charge, which would further extend the mileage-expiration date.