Are they absolutely relevant?

Do you folks put them back on after you take them off to do work?

 

The starter one yes if you don’t want it to fail prematurely due to heat. The one on the opposite side of the engine is mailing to pretect the motor mount. Same thing, heat will destroy it overtime.

 

The exhaust manifold radiates a lot of heat. After 20 years the wiring loom is mostly toast. It crumbles if you squeeze it with your fingers. I just replaced it on most parts of the wiring harness, since the engine is out at the moment. Yes, the heat shields are absolutely necessary and there are areas which need more heat shield.

 

If anything, more heat shields are needed. You may not notice an issue immediately if you don't replace a heat shield, but you will over time.
Since these vehicles are all near 20+ years old, the effects of heat over time are being scene. Don't remove any of the installed heat shields.

 

Yep, while you have your heads and exhaust manifolds off go ahead and remove the CPS cover and wrap that in aluminum foil also.