If you've held the itinerary, and then go to the My Info page -- the link is at the right end of the dark blue bar at the top of the shop for flights page. Log in and you will see a list of reservations you are "holding" with a number. They might be able to find your reservation that way. What kind of fare are you getting with you special Y -- better, I assume than the $1800 that I was finding through AUS?
Not flying DTW-NRT is probably the best way to maximize mileage and adding in HNL does even better. LAX-NRT is 5451, LAX-HNL-NRT is 6374, DTW-NRT is 6400, DTW-LAX-NRT is 7400, DTW-MSP-HNL-NRT is 8300. I do think you would have to overnight in HNL if you build it in.
HNL is not included in the free upgrades destinations -- we all wish it was.
Elite Upgrades are subject to availability and are valid only on Northwest and Continental flights within the 48 contiguous United States and to Alaska, Canada, the Caribbean, Central America, and South America. Select Continental Micronesia flights are also included. Continental flights to/from Central and South America with a BusinessFirst cabin, and all Continental Micronesia flights with a BusinessFirst cabin, are not eligible for Elite upgrades.
The link to this information is:
http://www.nwa.com/freqfly/elite/benefits.html