greetings, other than visual purposes (and making a good place for mice to nest), does the plastic engine cover serve a purpose, and more importantly, are there any potential issues to removing it & leaving it off?
I've hosed down my engine for 11 years now. If you are fanatic about keeping the engine bay clean, the shroud does ensure that water won't run down the ignition coils and into the spark plug chambers. As a fanatic, I know this all too well as once I had to have my chambers air "vacuumed," pressed and cleaned after a overly wet encounter with my HET. Some cars you can get away with the garden hose, and some you can't.
I kept mine on. I got a lot of dirt and other grime from road spray on the engine, and that cover helped keep the coil tops and wiring cleaner. The first time I took it off I broke the two plastic retainers but didn't replace them. I also once had the one valve cover stud unscrew instead of just removing the acorn nut
Besides keeping things clean in the spark plug wells, the covers help keep engine noise down. This is very important on GDI engines as the fuel injectors are very noisy on those types of engines because of the high pressure those injectors run at.