The front shield, seems to me, is pretty much just for looks. I picked up to older Q300s, one with and one without. Since one would be on my sister’s porch, she got the shroud while the other is going out to our church property in the wild interior of the state. Since that one is basically in a commercial setting looks don’t matter that much and it is one less thing to break or have to clean.
The piece that holds the tank on those older Q300s DOES seem important to me. Interestingly, one grill I got had a metal holder (rusted) while the second - presumably newer - had a plastic one (not as strong). On the newer Q3200, as noted by others above, Weber ditched the holder in favor of just a strap attached to a base holder for the tank. If you move your grill at all, I really think you need something. An improvised replacement might even be better - and probably a lot cheaper- than buying another strap/buckle from Weber.