Lori:
I have to say that I am a CO elite and it "appears" that it is easier for CO elites to get upgrades on NW flights than MW elites. This is just my feeling from reading posts. Also, it appears NW requires NW elites to buy a much more expensive ticket for it to be upgradeable. I can only say that as a CO elite, I have upgraded tickets to SIN, BKK, and TPE, all of which were less than $1,000 RT from NYC with CO miles thru OnePass. The only requirement was the availability of upgrade seats.
I would suggest first finding out what is the minimum fare NW will allow you to upgrade from. Perhaps you could post this as a question on the Board. Be specific as to your destination. I suspect BKK and SIN are the most difficult to upgrade to, but I think it is at random, depending on when/how many seats NW decides to release.
If you are thinking about NRT, then seriously consider using CO thru EWR, even though it is the long way around. IMO, BusinessFirst is superior to WBC. There looks like a lot of upgrade seats available on CO from EWR to HKG when this route opens in March, if HKG is in your plans. I hope this helps. If not, e-mail me.
Ed