Burning pump gas causes buildup no matter how perfect the air / fuel mixture is. There are byproducts of burning things. Look in any engine, even that running a very tight AFR and you will see buildup. That said, its currently impossible to build an engine that runs perfect AFR at all times anyway, so that argument is pointless. This is even less possible in positive pressure engines (turbocharger, supercharger... like most companies are moving toward) that require richer AFR for proper combustion without detonation.
One nice thing about Ethanol / methanol is they have a cleaning effect toward carbon buildups on the surfaces they contact... often acting like running a cleaner into your intake.
In any case, Iridium plugs are ~$12/ea and since that stuff likely came from a meteorite, it won't be around forever (might outlast the ICE though). Even though they may be rated for 100,000 miles, I wouldn't run them that long. In any high power / envelope pushing motor I wouldn't run them for more than 15,000 miles. Cut that by 1/5th for copper plugs. Feel free to double or triple that for your standard Camry.
Sure, your oil might lubricate stuff for 100,000 miles, but would you use it for that long? Spark plugs move out of gap, get carbon and metal buildup, increase their resistance from wear, and can basically completely change how a spark is firing based on charge/dwell time of the coil over a few thousand miles.
Moving to something that was more efficient, more consistent, provided for a more consistent ignition, and kept increasing our envelope of efficiency could definitely be worth it.
I just wonder... can you push start a car with these? :)