I guess with the rate of air leakage around my windows and doors, not to mention the sheer size of those windows (uninsulated space), it would have never occurred to me that insulation could help keep the plane warm inside. Do you really think it does?
I do not. Only when you reduce the rate that your air leaks "changing the air in your environment" to less than your heating system's ability to replace that vacated air with WARMED AIR, will your cabin be "toasty".
There's a bigger consideration (at least with fiberglas -the ONLY item that you could say is "reasonably priced"). As drafty as these airplanes ARE, at 120 mph (give or take), how could you POSSIBLY expect there to NOT be a few thousand strands of glass threads flying around inside your cabin whenever the prop is turning? That's in the very air you suck in about every five seconds! Any piece of glass fiber you snort into the cilia that IS your respiratory system is never ever going to "get back out". It's trapped there FOREVER. Nobody apparently THOUGHT about this before about 1970. Would you go up into your attic in a tee shirt, no gloves, and without a respirator to keep the 'glas out of your airway to save four dollars of oil a month (SOMEBODY is gonna go "yuup, do it all the time!" Well, good luck with that, fella!)? Okay, looks like the 'spensive stuff is the only viable option. Will THAT work any better? Well, somebody that spent a couple Grand on doing their airplane with it is going to insist it DOES, but I am unconvinced, as far as "heating" is concerned. You still have to stop the drafts, or you is gonna be cold. Case closed.
As far as "noise level"? Save the money and grief of insulation for a better set of hearing protectors/headphones, and roll up a set of E.A.R. expandable foam inserts before you snap your stereo headset over your head... That's the only thing that is going to garantee that (even a MY age) you'll be able to still hear a squirrel fart at fifty yards, in the woods.
Really... admit that ragbag airplanes are going to require hearing protection, anyway. Even with insulated sidewalls (Cripes! can you describe for me "how to build a DRUM"? You are sitting INSIDE one!). Remember too, that any strand of fiberglas that you inhale is GOING TO BE there "for there duration". I haven't put fiberglas insulation in a recover job since 1976. Can't rationalize doing so.