The actual shops within the Madinat complex are not worth bothering about, a lot of small shops all sellling a lot of crap in my opinion. However the madinat is close to the Mall of the Emirates, although I am not really a fan of shopping in Dubai.

The Park Hyatt is a good location for the Airport and the Deira City centre shopping mall is within walking distance. i think there may have been service issues there but these may have been teething problems, there are threads on the Hyatt board. I think for 1 night through Amex it could be a good choice especially with the 4pm checkout.