It's certainly an interesting question and the core themes seem to be chemicals or not and what else to do

OK so heres what we do and mostly our issue is dust because in SA it does not rain so mud is not something we have to deal with that much(sic)

I use a Karcher on the low pressure setting with the engine on so basically no pressure at all with the intent to flush out anything building up. From 15 years of doing this with 4WD never put any water pressure into bearings such as idler pulley's or electrical as this will come back to haunt you regardless of if it is a Toyota or Disco and I know from having done it to both.

Outcome is to live with an engine bay that does not look like it did off the showroom floor. Just try and keep the buildup of muck off stuff. Tend to leave the electrical stuff alone and wipe with a dry rag only

Gordon's book has a great section on cleaning and prevention of water and dirt ingress into electrical connections etc. I follow this in detail

Regards

Rob