The thin paper gaskets mentioned are still available from FelPro for a 440 3x2 carb setup as the first year they used an aluminum intake manifold, which was later replaced with a cast iron unit. The paper gasket keeps things from degrading with the hot/cold cycles as the dissimilar metals "move" with the expansion and contraction actions. These usually are not issues with the cast iron intake manifolds, but they can be used there if desired.
What I like to do, even on the non-metallic intake gaskets, is to take some high temp silicone and spread it all over the surfaces that the gasket has that will contact the head or intake, paying special attention to fill in the "beads" in the material with sealer. Then I take a gasket scraper and smooth everything out so the beads are full of sealer and a resultant thin layer of sealer is everywhere else. I'll let that skin off prior to assembly too.
What filling the beads with sealer does, in effect, is make the gasket a "print-o-seal" style gasket that many OEMs started using in the 1980s, where they use robotics to put a thin bead of sealer on the paper gasket. Then, when the gasket is compressed by the bolt torque, it's a really secure seal. The additional thin coating of silicone will make things easier to clean up later too, if and when that might be. To me, that's just a little extra insurance.
Silicone and fuel typically don't go well together, at least with raw fuel. In the case of the intake gasket, that's not an issue unless there's a flood, in which case you might not worry about the intake gasket anyway. I definitely like it better than the weatherstrip adhesive things that many used in the past! Everybody has their own perferences and that's fine--just don't see me get excited about scraping valve cover gaskets from the cylinder head OR the valve cover where weatherstrip cement was used to keep things in place.
As for the fiberglass "insulators", the Mopar Performance/Direct Connection Race Manual indicates they are there for vibration suppression so the metal gasket does not crack from vibrational harmonics that might exist in some operational situations. In many cases where they were discarded, I don't recall anyone saying they had any problems, but if the Chrysler engineers put them there, they had a reason. Pretty easy to replicate them with some fiberglass insulation and some heavy gauge aluminum foil.
I know there are some small block Chevy intakes that use an open area the runners with a cast-in base area, effectively duplicating what Chrysler did. In the case of an a/c equipped car, the air flow under there would be much reduced from what it would be if there was nothing between the thermostat and the oil pressure sending unit, air flow wise. I doubt seriously that either way would significantly affect engine performance in a street motor. More cosmetics than anything else, especially as the hot engine oil is not contacting the bottom of the intake anyway, as in the Chevy V-8 (which also has a sheet metal shield to keep the oil off the bottom of the intake and the heat crossover passage). Exhaust heat is still going through the intake's crossover passage anyway, even if the heat riser valve is full open.
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