Thanks, that is helpful stuff.
From how I see it:
Google has all the data we could possibly want, but may not want to share it all with us mere mortals, or may filter in ways we cannot control.
So according to your post, the broad match is good finding PPC keywords, but you'd want to use something else (exact match?) for finding organic keywords.
The other paid software may not have enough data, but in some cases may have more helpful tools.
The Adwords data wouldn't necessarily be free, because I would probably want to use the API.
I was close to signing up for a year of WordTracker but now I am thinking maybe not.
Re: Keyword difficulty.
From what I've seen, all tools seem to use pretty simplistic measurement. Is "number of search results" the best the industry has?
To me, is a keyword going to be easier because it has 224,000 results instead of 3,645,000 results in Google? I'm not sure. That really depends on what's in the top ten.