Also, can someone tell me how reliable/ useful the google keyword tool is in evaluating a domains value?
All else being equal, it's better to see high numbers in Google. But that's only one factor among many. Obviously, the extension matters, for instance. But most buyers are responding (at a gut level) to variables other than Google search stats. So you'd do well to consider what those other factors are. Often they correlate well with search volume, competition, and CPC. But often they don't. You'll also need to ensure that you're interpreting the numbers correctly. A common mistake is to fail to distinguish between broad, phrase, exact, global, and local. Many domainers frame their "wanted ads" in terms of Google stats. They're not wrong to do so, and it does help to focus attention on a smaller selection of domains. But to some extent, it's just human nature to stick close to something quantifiable because it seems scientific and assured. Ultimately, raw data is only as scientific as the person interpreting it.
Sorry not to supply a simple answer. Any simple answer would be wrong.