As said, and you thought, your biggest improvement is in maintenance. Goes down to virtually zero after the swap. Assuming you don't have electronic trouble with the unit, it can last forever. Many of us have had them in Broncos, and I've had them in other cars for decades without trouble (that wasn't caused by me that is, but that's another story...). Yet over the years with so many sold, there are certainly trouble stories as well. So nothing is perfect.
And yes, under the right circumstances it can run a little better and maybe get a tiny bit better mileage. Power? Hard to tell. Might be good for a couple of HP but that's hard to feel unless your butt-dyno is pretty finely tuned.
As said too, points work, and worked very well for many years too. But I still feel the Ignitor (as well as other conversions) are an improvement over stock points.
The good part is that if anything does ever happen to it, you can swap your points back into the distributor in a few minutes and be on your way again.
Every modification I made to mine (ignition, intake, carburetion, etc...) improved the overall feel and experience of my Bronco. But I would never say they made much of a difference in overall power or mileage.
But each thing that did improve power, didn't seem to hurt mileage. So that's a net good thing!
To add a little to what Steve said, HEI's are great, but in the early days of our conversions there were more sob stories than happy endings almost. Steve's a lucky one from back then, but in truth there have not been any bad things said about their performance or reliability in a couple of year snow I don't think. At least I don't remember hearing any here?
I still don't like the big huge cap, but there's no arguing with the technology.
I can't tell you that an Ignitor II, or III is actually "better" than an Ignitor I from a purely horsepower or reliability aspect. But the II and III have some added features that do improve the spark energy, and may contribute to a better running engine.
The Ignitor III is also a multiple-spark ignition control module, so has that added benefit that should help combustion efficiency especially in older design cylinder heads.
Might notice it more in a traditional stock head, vs for example a GT40 head.
Bottom line is the Ignitor is a reasonable cost option and anything that eliminates one more level of maintenance is a good thing. It's the only real reason I did it, as my points worked very well. Because they were fine-tuned to perfection pretty much every other week!
Maybe make sure your old distributor is still in good shape however, so you don't go throwing pigs feet at a sows ear.%);D Or however that old saying goes.;D
Good luck.
Paul