I've yet to use chemicals, even the sample stuff that came with the rig, and I do something simpler than the Geo method. My black tank is a holding tank. It isn't a septic tank, and it isn't a place where bugs go to meet, play, date, and have a night on the town. It is a place for stuff to sit until I dump it.
Empty the tank, hold the toilet open, squirt some Dawn dish detergent in the tank. With the grey, pour some hot water with detergent in as well. So far, when dumping, this has worked pretty well for me, and when I do the smell test by opening the flush valve with the bathroom fan on, it doesn't stink, so it seems to be working. Dawn dish detergent is made to break up grease and other gunk on dishes, and poop is pretty much the same thing.
My next rig, I'm either getting a Camco cyclone vent (uses the Venturi effect to suck stuff up and out) or a solar powered fan vent cap. Either one will help ensure that any bad smells are exhausted out the roof.
I do like the 35+ CFM computer fan idea, although the "Lil' Stanker" is not sold anymore. I also believe that at least some type of item, be it Camco's vent, a solar fan, or a computer fan connected to the 12 volt system should be standard on at least the black tank, if not both the grey and black tank vents.
I also agree with you on the aspect of modding... it seems the mods I have planned or the mods I have done are stuff that should have come from the factory. Things like a three stage charger, an accumulator tank (to minimize the late night "burrups" by the water pump), a voltmeter to accurately gauge how the batteries are, and even having the same key work both RV door locks should be things that are standard.