Hi Carl,
For the first 5 years (1965-70) that I owned my now restored '36 Chevy PU I ran it as a sbc powered "rat rod". The engine had home made headers that I made copying the Doug's Headers "Tri-Y" design in a quest for streetable torque. There was no unpleasant cab overheating, even in summer time because there was good air flow through the engine bay..
In my experience in the hot climates where I have lived header equipped sbc engines in well ventilated engine bays don't cause any problems. No exhaust leaks, no cooked plug wires, no plug access problems and no cab overheating.
The performance gains are documented in the magazine tests. The example I included documented torque increases of 26-53 lb-ft, a very substantial gain. In street driving torque is what we feel seat of the pants, not horsepower. I'll take it. Others may say "no thanks".
The "eye candy" benefits are questionable, depending on personal preference.
I go to very few shows and cruise ins but at the ones I do go to headers are very popular so they must have some kind of appeal.
