Hope you don't mind, I moved your post over to the PPC forum as you've raised some interesting points and I think PPC could be an effective route for you.
It sounds like you have been doing PPC for a while, so should have built up a good bank of data, ie what key words work well for you, which negative ones to add.
Surprised why you think it's been a waste of time over the years though, because if a PPC platform isn't performing for you, drop it and move on.
If multiple platforms aren't working, and you are generating traffic but no conversions then that sounds more like a landing page issue, or untargeted traffic.
Most platforms these days are fairly straight forward to tune. In Facebook you can very quickly get granular targeted information, whilst Google relies on some tuning, keyword performance, adding in negative terms so they won't trigger any ads.
Each PPC campaign should be (assuming that's the objective) tuned to leads and conversions. Every click needs to be highly targeted, rather than paying for browsing web traffic!
So that leaves your landing page(s).
Have you done any landing page analysis? Do you send everyone to your home page, or to a particular landing page per campaign? Have you tried any split testing?
Check your analytics which will tell you everything you need to know about bounces, how long people were on your page and where they went next.
If you are sending people to your home page, imho when landing on it as a fresh visitor it comes over as very busy.
There's lots going on, lots of things trying to grab my 3 seconds of interest before I carry on surfing.
But your own data will tell you that. Compare the years of PPC data, analytics and customer conversion data and see which pages are working and which may need a tweak. Rinse and repeat until the leads start coming in.
Stats wise, if you set up each PPC's relevant tracking code for conversions, then this should match roughly any analytics.
For your industry, I'd be surprised if PPC didn't work, it should be more a case of making leads viable with enough margin for profit.
Does that help?