What's the best outcome you've gotten through buyer or customer research? Was it really worth all the effort / money?

Absolutely worth the effort! A great example of where extensive qual and focus group research really was worth it was when we launched Uber Pro. In initial product strategy discussions, the internal team was exclusively looking at financial upside or discounts as rewards. But what we learned through qualitative research was (a) that they really wanted to feel appreciated for all their hard work and (b) their primary motivation for the hard work was providing for their families. 

After unlocking both insights, those two became critical to the product, program, and marketing design behind the initiave. Post launch, we saw two main outcomes: 

1. Drivers were initially skeptical but then much more receptive to the program because we showed we were supporting what they cared about most -- their family -- and wanted was in their best interest.
2. If you take a look at the press that we got as part of the result, you can see that helping them provide for their family via access to free college programs became one of the 2 main messages that was picked up. 
3. The press showing our support of drivers & their families ended up having a positive master brand impact with multiple audiences.

I really attribute the 3 outcomes above to doing extensive research as we wouldn't have landed at that strategy without it. 

Yes!! Product Marketing isn't doing it's job properly without it. Also, it's a lot of effort, but doesn't always have to be a lot of money. It doesn't cost anything but time to get on the phone with customers, or listen in on sales pitches (these are some of the places you can get the most early stage information from).  

One of my best outcomes of really digging into customer issues, was when I was working on a product that had something really weird going on in the customer base. Half of the customers loved and embraced the product, and half of the customers hated it. Also when I looked at the feature requests that were coming in, most of them were coming from the people that hated the product - but what was even weirder is they were features that didn't align to what the product was built to do. It was then I realized we didn't have a product problem, like the company though - we had a positioning problem. Anytime I see that big of a polarity in the customer base for a product, my first thought is that the product is fine, it's the positioning/messaging that's off.

So I spent months, with my PM counterpart, connecting with customers, sales, prospects, analysts, and the general market to find out, what was the underlying painpoint they were hoping to solve with it - and then finding out how we positioned the product. What it came down to is that most of them had the same exact pains they were trying to solve, what was wrong is that some of the reps were positioning the product incorrectly - we had the wrong messaging in our marketing material as well. They were making the product out to do one thing, when it really was meant for something else. This was a company wide issue, that when the product launched, we didn't do a strong enough job getting ahead of (actually the product didn't have a dedicated PMM to it at launch) - and so this product's incorrect positioning caught wildfire, because it was selling. People were buying it off the incorrect positioning, but then they were turning into unhappy customers that wouldn't expand/renew.  

Once we enabled everyone correct, and retrained/reset the organization on what the new messaging/positioning is (which wasn't a drastic shift) - we saw a HUGE change in the sales motions, the satisfaction in pre-sales conversations went up, and the customers who were buying it off of the correct positioning are much happier. And, best of all, the growth rate of the product didn't go down. There were far fewer "incorrect" feature requests as well, because the proper expectation was set.

People don't always realize how crucial product marketing is to the success of a product - and that just because something is selling, doesn't mean it'se selling correctly. :) 

So TL;DR - Yes, it's absolutely worth it!