What I'm trying to say is if your phrase "red wooden widgets with wrough iron imprints" does well on overture and you have great ROI, but you need more clicks cause you want to expand - it wouldn't be wise to ignore adwords. And vice-versa.
The ROI might be lower, but if it's still positive (and for such specific term it better be) then why not use both?
I have a few narrow keywords that covert every 10th visitor, but I only get 3-4 clicks per day on adwords with high CTR. Why wouldn't I do the same with overture?
I mean, if I make the phrase broader - the conversion would drop, so I need more market for the same search.
On a personal note I find Adwords traffic does convert a bit lower than Overture but I'm sure every account is different.
I have literally hundreds of keyword phrases on OV that I pay (paid) .05 a click for because there was no one else bidding on that term. On adwords, I have very few of those because of the broad match. I would imagine that adwords makes bonus money off that and wouldn't need to raise bids (I hope)