I think your upgrades on cheapy domestic flights as a low-level elite will be much more apt to happen on Northwest than some other airlines. Flights to the west coast have a lower upgrade level.

With all the merger rumors certainly everything will be in flux - no one can know what the next few years may bring!

One good thing with NW - is you can still earn qualifying miles on Delta (100% qualifying miles, but no upgrades) and Continental (some upgrades, but only 50% qualifying miles when a cheapy fare).

Good luck!