Under hood insulation

I would tend to agree. The likelihood of the plastic tabs all melting in a way that allows the sheet to drop over a fire is slim.

I noticed 0 difference after removing mine. Most of the noise comes from elsewhere.

 

Plus on the 3.4 at least it could only "drop down" between zero and 2-3 inches. The intake, throttle/cruse/trans cables, evap canister and clutch/brake cylinders would all hold it up.
When I had mine out to coat I could tell a difference in sound but it was very slight. The kind of thing you forget about in a few days. The main reason I preserved it was Toyota really skimped on the paint. There was a good nine square foot or so area under it with no color coat, just the gray primer/sealer.