I really don't think Wendy as worthless. I think she has a bit of the shine to her and its both her and her son that the hotel wanting "corrected" so they cannot spill the savory secrets of the Overlook's past.
*** SPOILER ***
Remember the waiter telling Jack when he is locked in the storage room that maybe the hotel should have used her instead of Jack. Also, I think she has a hint of her son's ability. She is the only one that talks to Tony and there are flashes that she knows what is going on. Remember her out-of-hand reaction when Halloran calls Danny "Doc"? "How did you know we called him that?" she asks.
In the beginning, I think she is being the supportive wife ("We're all going to have a good time"

and refuses to see Danny's side of reluctance going to the hotel. Its only after Danny is injured, where she is hugging him, that she turns to Jack and says "You did this." She is no longer the inactive wife; she is going to take care of matters on her own.
And after she sees the word REDRUM, she has shinings of her own of what the hotel really stands for.
EDIT: Also, she is the only one we see in the film doing work (i.e. checking the furnaces, cooking, etc.).
[This message has been edited by Big 12-0 (edited 7/14/2006 2:06p).]