Yeah, getting in the nooks and crannies is a pain.
If you spray the Gunk stuff on to where it'll get everywhere, I'd do a very thorough rinsing.
I was steaming some stuff in the engine compartment of the '84 RX-7 yesterday, and there was a definite limit to what it could do. It works OK on regular grease and dirt, but baked-on stuff just didn't budge until I got some solvent on it. Sometimes you just need a chemical. I dunno how well the steamer would work for a rinse...and I'd be a little careful about protecting yourself as the combo of pressure, steam, and the Gunk might not be the friendliest stuff.
I always end up using a bunch of brushes and a zillion swabs, but these are engine compartments where I don't want to be spraying a lot of water for one reason or another. When I'm not worried about the water I'll just soak stuff with the engine cleaner, let it dwell, and hose it off. Though I really oughta use the pressure washer for some of these jobs...I use the steamer more for limited areas where I can get right at the area in question.