If you don't have an immediate need for the AA miles (awards, million mile status, etc), then it can't hurt to wait. Once the points have been converted, there is no going back. So if you find out later that you could have used the SPG points for a hotel stay, then your just out of luck.

But I doubt that SPG will be taking away the points-to-miles conversion awards anytime real soon if that was a worry. So you don't have any real risk in waiting.