Hi DC Glenn,

First, a simple best practice: Never invest heavily in SEO before testing the keywords with PPC. If its low competition, the clicks will be cheap...well worth a few hundred dollar test....
Regarding your Goldmine...

The real question becomes commercial intent of the searches as well as the credibility of the keyword tools you are depending on.
There are 3 main types of search queries.
1. Informational - top and middle of the funnel looking for information
2. Navigational - looking for specific content on a specific website
3. Transactional- bottom of the funnel looking to buy right now. (These are the goldmine keywords)

Without knowing what types of keywords you found, I cannot tell you whether you really landed on a goldmine. My instincts tell me that you are probably missing something...but there is a very simple way to find out one way or another.

Run a limited ppc ad test on Bing for those keywords. The point here is not to drive conversions as much as to see how much search volume there really is. The reason I recommend bing over Google for this is because Bing will report to you on unclicked impressions, whereas google will only tell you about the queries that earn clicks. (it is estimated that your ad shows 20x more than you see in adwords due to queries with no clicks.)

Once you have a baseline for the queries and impressions, you can multiple that by 4x and you will have a pretty good idea how much actual search volume there is... vs. what the tools tell you which are algorithmic guesstimates and rarely accurate. You will also be able to see how those visitors behave on your site (or just launch a quick unbounce landing page with a basic sales pitch trying to get some optins.)

Once you run the bing test, you will know if its worth investing deeply in SEO.

A few things I would note...I you did indeed land on a goldmine...expect it to get discovered within the next 4-6 months. These opportunities rarely last. So, prepare for it to dry up.
Two, don't assume the competition you see on your searches are indicative of search behavior across the country. The world and this country are really big places and its easy to get stuck in your own filter bubble and think competition doesn't exist that does. (i.e. they have been investing in SEO for months or are a stealth startup with huge ad budgets... and you just havent discovered them yet.)

Further, if you really think you found a goldmine, dont share it with anybody. Not me, nor anybody on clarity or anywhere else... it is so easy to compete with you without it being able to be traced back to me. so, so easy!

Good Luck.