I've got an '05 RX330.
I drove over an errant rock left by construction and it tore my engine splash shield half off, was dragging it for a while and then someone helped me unbolt and remove the rest of it.

How important is this part? I live in Alaska and was told to get it replaced by the winter. Do I need it if I'm going to be driving gravel roads and/or in snowy conditions, etc? Do I risk damaging the engine if I don't replace it, and/or how much does it affect my fuel efficiency?

I've been trying to find a replacement part. I'm attaching a picture of my own plate, it looks similar but not identical to a replacement part on Amazon:

How identical do they have to be to fit?

 

Given the OE part is $350+ you'll have to decide if taking a chance on that Amazon part is worth it. Without that cover snow will pack up into the engine bay area not ideal I'd replace it.

 

I prefer them strongly; they keep debris out of belts and pulleys, they direct cooling air to brakes (not a big deal for you), etc.

I’d definitely get that Amazon one for the price, if you can’t repair that one or get a pick’n pull one affordably. I have repaired them with epoxy and bracing; not sure if that one is repairable or not; the front could be braced but looks like a substantial amount of the rear and mounting points are gone.

 

When mine started falling off, I secured it with zip ties. You have to get creative, but it worked until I found a replacement.

 

I'd replace it. Keep the old to compare it thou. I don't think it critical compared to the front one (below the bumper) Neither my wife or I ever had a vehicle w/ engine shield before.