Micro niche keywords traffic - a game of luck?

Hello all,

I own many ebooks about keyword research/micro niche sites and all of them directly or indirectly says that not every keyword you build site around will bring you traffic / earnings.

I suppose there is no tool on market which will find you long tail keyword which would make you money for sure. Only Google Keyword Tool's Global/Local monthly searches isnt enough I am sure(read at the end why), that would be too easy and everybody will earning money with adsense.

So I ask, how do you analyze keyword found in GKT further to see if its worth building site around?

1. Number of advertisers on first page for that keyword?
2. Google Insight "Last xx days" data?
3. Adwords PPC campaign?
4. Adwords Traffic Estimates?

Or is it all luck?, find keywords in GKT with min 1000 searches a month, low competition on first page, low allintitle blah blah, build site around and hope it will receive traffic? :confused:

I own #1 position site(promoting aff product) on Google for long tail keyword which gets 8,100 exact searches per month according to GKT, and I have 30-40 unique visits a day. I earned 200% net of my investment from it, but still, thats not traffic I was looking for.