The Google Keyword Tool is SUPER helpful for building a foundation for your keyword research strategy. At the end of the day, these search numbers are coming straight from the horses mouth. You can filter down to a hyper-local level and see which keywords are getting the largest search volume. Plus, with it’s integration with PPC you can get a quick idea about commercial intent by looking at the bid and competition metrics. How much are people bidding on KWs, higher = more likely to generate a return. Usually its aligned with search intent. That said, the trending data is a little less reliable. I would still use Trends to analyze the popularity/ seasonality of KW search volume.
After the Panda update rolled out, the latent risk in such a strategy could (typically would) vastly exceed the direct cost of the content, as poor pages on one part of a site could drag down the ranking of other pages on the site which targeted different keywords. Some sites have seen their search traffic fall over 90% with their ad revenues falling even faster. Demand Media went from being worth a couple billion to tens of millions of Dollars. ArticlesBase.com sold on Flippa for $80,000, but was making over $500,000 PER MONTH in profit before getting hit by Panda. Many other Panda-torched sites like Suite101 have simply went offline.
Long Tail Pro is a keyword research tool that helps you quickly find low competition keywords for your website. In particular, the tool is built for people doing SEO (search engine optimization) as opposed to people doing paid ads (Google Adwords PPC). I'm sure there are some advertisers that use the tool for paid ad keyword research, but the tool was built for SEO keyword research.