Gary
Modern cars are a pain to clean inside the engine bay as they are increasingly cramped and fidley but I do the following.
1. Remove the painted plastic engine cover on the VE motor and wash it in warm soapy water and dry.
2. Any oily surfaces (but NOT painted body panels in the engine bay or any wiring or coolant hoses or belts )
Get a roll of paper towel and some kerosene. Dampen a piece of towel in the kero and wipe over the surface. Keep doing that until it is clean then wipe it over with a large damp cloth soaked in hot water and detergent. Keep rinsing the cloth as you go.
3. All Non oily surfaces.
Wipe over with a damp cloth which has been soaked in hot water and detergent. Also use some paper towel for this. Keep rinsing the cloth well as you go. For painted body panels finish off with a clean sponge soaked in plain water.
4. Get a bottle of AmorAll Protectant or any other similar product for finishing Vinyl and plastic surfaces. (The cheaper imitations are just as good for this).
Get a piece of cleaning sponge, add some Protectant fluid on the sponge and wipe over all the black plastic surfaces you have already cleaned. (Don't do this on the painted engine cover or on wiring). This will also act as a final cleaner. You may pick up some grime on the sponge as you go so wash it out as you go or throw it away and get a clean piece. Also do the coolant hoses lightly. This will brighten up the black plastic surfaces and they will be easier to clean in future.
5. Replace the cleaned engine cover and you should be done.
6. Each time you wash the car open the bonnet and clean the water run off channels and edges of the bonnet.
Also look for anything in the engine bay that looks like it needs a wipe over with a paper towel dampened in kero, or by a clean damp cloth, and do it. You will need to re-do the Protectant from time to time but it is fast and easy (and also works on your cleaned road tyres by the way).
If you want to see if this really works then have a look at the engine bay of my (now sold) previous car - 2004 VY II S. The picture was taken in Apr 2012 - 7 years and 10 months after I purchased the car new. It's dead easy to keep the engine bay clean like this for many years if you don't neglect it. My new VE SV6 series 2 (June 2012 ) will get the same treatment.