This is a tough question. I have always wondered what all the water that gets sprayed into the Spark (during a rinse), would do to it if you did it every single time. I wonder what percentage of the metal components aren't painted or aren't made out of stainless steel. I wonder how many people wash down the engines in their cars after being parked at a beach parking lot all day (salty air) assuming a big wave didn't rise up and over the car.
I only ride in salt water. No salt water has ever gotten inside (I've never flipped the Spark or taken a wave over the handle bars). I pulled the top off and examined it. I couldn't find any salt anywhere.
When my Spark was in the shop getting its oil leak fixed, they test drove it in salt water to test for any issues. They didn't thoroughly wash and dry the outside of it (like I do), there was dried salt on top, in the back (in the slots between the plastic pieces), when I went to pick it up. You could easily spot the salt from 5' away. That salt had dried out of the salt water, over night. I had taken the top off after I got it back from the dealer. No salt inside, no rust.
Neither dealer (both along the coast in areas in which everyone only rides in salt water) that I talked too say that you need to completely wash out the inside after every single ride. They do say that you should spray all the metal that you can with an anti-corrosive spray, and to keep an eye on things. You can look inside the access panel or through the oil port. You can use a good flash light and look around for salt, rust, and corrosion. Take a look at the bands that hold the hoses on to things and take a look at the mounts that hold the engine in place for example. I think if salt were accumulating in there, you'd see some sign of it.
When I come back from a ride, no water comes out and I don't see any water in the Spark. Then I wash it. I always get some soapy water in the Spark. It goes down the air intakes and runs down the inside center along the bottom. I take my wet/dry vac and vacuum out a pint. Then I leave the access panel and oil panel off and what little is left will evaporate over night.
I'm not telling anyone not to wash the engine compartment out. I think everyone would agree that if you flip it or take a wave over the top, you should wash it out. Again here is another good reason to have an additional access panel under the seat. It does make me wonder that if Sea Doo was so concerned about washing the engine down every time, why didn't they provide better access to it? An access panel under the seat and/or an additional access panel on the starboard side?