I use a sprayer that connects to my air compressor and draws the Gunk
or whatever de-greaser I'm using out of the gallon container. It puts
it  just where you want it with little overspray. Keep my engine
relatively clean. I too find working on a clean engine much easier
and, yes, it's easier to diagnose when things go wrong. I am also a
fan of WD-40 and brake cleaner when used in moderation. Mind you, my
van is no show car by any means, but I try to keep up with keeping it
clean even when it's not running.

I also have a theory that half of the parts that "break" (on anything,
not just engines) is only caused by dust and dirt accumulating on
them. I can't tell you how many parts or things I've "fixed" just by
giving them a thorough cleaning. This is especially true of
electronics. I've gotten many a "broken" TV or computer either by
finding them in the trash or having a friend give them to me. All it
took to get them going again was a spray of electronics cleaner.

-t