I have/will continue to clean the engine on all my vehicles. Its a lot easier to spot problems before they cause trouble, easier to work on, and in my opinion a pride in ownership type thing.
I did a 4.0 over the summer, had once of the sensors get wet in the process and it would not start (kept getting a no bus on the dash). So i will say this:
Inspect the engine/harness/vacuum lines for cracks and damage (replace now, you should do this anyways)
Plastic bag your intake (or leave the factory setup in place and dont spray it)
Cover all electronics (duh)
Cover all sensor connections
^^ Avoid spraying these two items
I like to use Meguirars all purpose cleaner (green liquid, about $15 at a store for a gallon and it lasts forever). Dilute this 1:1 for real bad stuff, 5:1 for regular duty and 10:1 for maintenance. Use a $1 spray bottle to spray it on, agitate with brush and rinse off with garden hose pressure. Rinse (literally) and repeat as many times as it takes to get it clean.
When your done, start up the heep and let it run for 15 minutes to dry everything off. If it doesn't start, use contact cleaner and inspect all your sensor connections.