All excellent suggestions.
If your folks are curious as to where their London Bridge ended up, you could take them to Lake Havasu.
If you do make it down to Tombstone (very cool - O.K. Corral, Boot Hill, etc), you may consider taking a slight detour to check out Kartchner Caverns State Park. Well worth it IMO. The tours book up quick though, so it is recommended to make early reservations.