I don't like owning or working on "filthy" engines.
If its filthy it's not "beautifully maintained" as mentioned above. (Maybe it's just me.)
I'm not recommending for everyone, but at least twice a year I spray my entire engine compartment with degreaser (while hot) loosen dirt with a parts cleaning brush and pressure wash with very hot water. Obviously I don't blast it into sensitive areas, but I'm really not shy at all.
I then start/warm-up and drive it to dry it off. Never had problems.
(Much more pleasant to service when the time comes)
1999 Caravan LE, 3.3L, 300,000KM
2005 Saturn Vue AWD (Honda J35 3.5 V-TEC 260HP) 216,000KM
1982 Suzuki Katana,(ported/shaved head,11:1,4in1,KNre-cal/filters,cam,120HP)