The profitability of a niche term (without the above tools) can be determined by the Google keyword tool alone, by looking for keywords with sufficient exact monthly search volume, and the competition for the keyword among people conducting adsense campaigns. If the keyword has medium or high Adwords competition, good search volume, and low or manageable SEO competition (few competitors with decently SEOed sites using the term), it's a good keyword.
Other considerations affecting evaluating a buying keyword relate to the method of monetization (if using Adsense, choosing keywords with a CPC or $1-2 or more is advised), or the context of the search effort (is the searcher just looking for information, or to help reach a buying decision?). E.g., if it's a "product X review" keyword being searched for, the general IM consensus is that's a buying keyword, and could best be exploited by creating a review article or site to drive SE traffic to your product's landing page. Hope this helps.
