as a preventative measure against stripping threads(spark plugs, exhaust bolts, rocker shaft bolts)?
What's your opinion on this as it seems the Trick Flow heads don't have heli coil inserts as the Eddy RPMs have.

Forget that idea. Does a Ferrari, Lamborghini, Mercedes, Bugatti, Race Hemi or $100,000 Mountain Motor Pro Stock have heli coils? No.

They might be made of better grade aluminum than a mass-produced head, though... also not rebuilt nearly as often (well, maybe not the Race Hemi), so the threads are rarely "worked"

just me, but i would use studs in every "bolt" application, and a dab of hi-temperature anti-seize on the plugs. your mileage may vary.

Not till i had to would do that,

Use a good anti-seize on any bolts going into aluminum and you should be fine.
However if you do decide to do them on the spark plugs, go with the solid inserts and not the spring type. Use green loc-tite(sleeve retainer) when you install them and they will never come out. If you dont loc-tite them they have a tendency to spin out eventually.

Tell you what, you buy me any one of those things on your list and I promise to never put a helicoil in them.

I had to put a bunch of helicoils in a 727 when some jackwagon used the German method (goodentite) to torque the trans pan bolts and stripped a bunch.

Quality of the aluminum casting as well as if the bolt hole and threads are cut to the proper size will determine if the thread inserts are a good idea, one of the brands of race heads we deal with we have to put in time-serts right off the bat otherwise they will pull the threads, customer and or engine builder are not happy campers. Proper bolt depth is crucial in having aluminum threads survive and as said before if you can put a stud in there instead of a bolt that would be my first choice.

Stud it where possible. In places where that is not possible and the fastener will be removed frequently it would be a good idea to use an old school Heli-coil.

I ran a quasi-instrumented test (torque to yield and 10,000 lb tension failure) on the various types of thread inserts and the Heli-coil performed as well as or better than the other commonly found styles.