In most operator's manuals it states to avoid pressure washing or washing with a garden hose. The
electrical system, the
deck spindles, the
hydro trans - these would be the things to avoid getting wet.
I'm like you in this respect - I love to keep my work area, my tools, and my equipment clean. What I do to my tractor is this: after every use, I take a leaf blower to the deck to clear off the debris there. That's were most of it builds up. Then I go over the rest of the tractor from back to front, and then I blow air into the flywheel screen and watch until I can no longer see any debris coming out of the engine's cooling shrouds.
Once a year, I'll take off the fenders and the tunnel to give the frame and hydro a good hand cleaning. No water used here, either. Using a wire brush on the cooling fins of the hydro, and a plain old shop rag for everything else, following it all up with some forced air to clean out what's left behind. Lubricate linkages and such, reassemble.
An every few weeks, I wipe the exterior surfaces down and wax them. Yup, I wax my tractor. Keeps the paint looking great, makes for easy cleanup. I even clean and wax the backsides of the rims, both the front and rear rims. It's an annoyance of mine - I hate to have a clean outside of a rim with a gross inner side.
That's just what I personally do...