Do the speed sensors connectors ever need cleaning? I notice the input sensor has got some sludge on it, including over the wiring. The output one looks pretty dirty too.
Should i spray them with degreaser and hose them?

Also, can the wiring plugs be removed for inspection without throwing errors?
I assume theres no need to unbolt the sensors, they should be clean on the inside?

If there are no problems, leave them alone. You don't want water left in the sockets. If they need cleaning, do what you suggest but take them off the car to clean and dry them properly. Or just clean the outside with a rag sprayed with degreaser, and skip the water step. Should be ok to unplug them, just don't start or use the car with them unplugged.

Ain't broke? Well then don't fix it?