I agree - my break point is about $350 (with taxes, etc.) vs. 25,000 miles.
$180 - on NW to earn Elite (and 150% bonus) plus, some pts to Mile-a-Rama, etc.. seems like a nice option - on NW. If it was another airline - a little less value in "wasted miles" (which I feel I am doing on a non-NW/partner flight).
If it was $450-600 or more - use the miles. Since it is cheap and still available on award tickets - flights might not be too full.
Congrats on Plat for 2004 already! - I am planning out rest of yr - think I will just clear Gold. From MSP no dom flight is over 1600 miles.. Sometimes I wish I could "connect" from a small city and get extra EQM.