You're gonna need to cover up the alternator as the internals may rust over time if moisture gets in. If you feel you should spray the ignition coil, make sure the spark plug wires are tightly secured. You can get a pack of 'di-electric gel(is that right?)' for $.99 at the auto store to lock out moisture from the spark plug wire ends. I haven't tried Simple Green, but I'm sure any engine cleaner/detailer spray will work really well.
I think everything will be just fine unless you inundate the engine with the stuff! I hose my engine down every couple of washes to keep the grime from building with no problems. Keep up the good work!:sunny: