I've run into the same problem in the past and been shocked about the amount of keywords I had never considered that drive traffic.

Primary keywords are often head tern keywords, which show up most often in the Google Keyword Planner. Google leans towards showing high volume, commercial intent keywords. They do show a lot of informational keywords, and keywords with 10 searches a month, yes, but they are predisposed towards keywords that AdWords bidders would want to bid on. So keep in mind when using that tool who Google's customers are.

I believe it is most likely worth the effort because if you're seeing not a ton of volume for your keywords, it's possible that your competitors saw the same and might have decided it wasn't worth focusing on SEO for as well. That could be your opportunity. It depends on your monetization strategy and your industry. If there were only 10 searches a month for "how to make an easter basket" and that's your industry, it would be tough to make a strong case for spending a lot of time and money on that. If there are 10 searches a month for "oil field exploration companies" then each one of those people represents millions of dollars of revenue.

So in order for you to decide if it's worth it, you have to know what industry you're in and the volume of your keywords and keyword value.

Here's an experiment you should do to see if it's worth it. Take your top 10 primary keywords, and write one page of content on each, at least 1,200 words of content either in the form of a blog post or a service page. Put your best effort into it, and imagine your target market is already visiting that page. Wait 30 days and check on those pages in Google's Search Console. More than likely you'll see those pages bringing in traffic for keywords you had no idea people were using to find your site. Or on the flip side, maybe there's just no demand there. Either way, this will give you an early indication of whether it's worth it or not without you having to make a big expensive decision.

Happy to answer any followup questions!