And with the ignition systems we have today it’s harder to read plugs.
Not when it comes to pre-ignition. The tell tale signs of peppering on the porcelain are actually easier to spot with less sooting. The engine will tell you when it's not happy, you just have to read the clues.
I know a dyno session isn't cheap, but it's well worth the money. A lot of things can be determined in one dyno session, much easier than trying to hash things out in the car.