If you're purchasing from NWA, keep in mind that you get 3 miles/$ for purchasing gift certificates from giftcertificates.com, and through Dec 31, you get double miles for those purchases. Giftcertificates.com sells gift certificates to Sharper Image, so perhaps you could get 6+14=20 miles/$ this way?

NW does state "Not valid with any other offers or promotions", but I'm not sure that would cover (or whether they'd notice) using gift certificates for which you received miles to make purchases for which you receive miles.

In any case, if you want to try this, be sure to register for the "Holiday Shopping Spree" at their site and make all purchases through the "Worldperks Mall."

I hope this helps. Note that I haven't tried it yet. If anyone has successfully made this work, I'd appreciate hearing from you.

Ethan