You're right, the quanities of muscarine present are very very small quantities (in the samples analyzed), but the majority of the side-effects of fly agarics sound just like the effects of muscarine (salivation, perspiration, lachrymation)... I'm not sure what a threshold dose of muscarine is, but it seems like muscarine is a likely culprit based on the effects. I ought to see what info I can find on micro-doses of muscarine.
It's also worth noting that the side-effects vary from country to country... not surprising, as the Eurasian varieties are known to belong to a different clade than the North American ones. In fact, they have recently been seperated into Amanita muscaria and Amanita amerimuscaria. North American ones are much more apt to produce profuse sweating. Western European ones are anecdotally linked with greater nausea. Siberian ones are anecdotally linked with very few side-effects. Australian ones are known as the bottom of the barrel; very little of the good stuff (ibotenic acid and muscimol) with tons of nausea, sweating, and other side-effects. It's important to keep in mind regional variation when considering the side effects.
In terms of drying, you're absolutely correct that less than 150 degrees C is safe for the chemicals, but you're apt to end up with burnt mushrooms if you bake them at this temperature (believe me, I've tried). Around 90 degrees C seems to produce a better result (air circulation is critical). Quite frankly though, I prefer simple air-drying. I haven't noticed any substantial difference between the mushrooms I air-dried (in a box with a fan built into one side and a bit of ventilation) versus the ones I oven-dried.
With dried mushrooms, I agree tea seem the most effective way, although I really loathe the flavor. I prefer my drug teas to be bitter; opium poppy tea doesn't bother my taste buds much at all! Fly agaric tea just makes me cringe.
My absolute favorite way to consume the mushrooms though is too sautee fresh ones with garlic and onion, and cook them into just about anything you can think of. I really miss them now that they aren't in season and I can't cook a few slices of cap into all my meals (they're delicious, and at low doses they're a truly wonderful tonic). I had the forsight to can and pickle a couple jars which I'm rationing to keep me in supply until they come back in season this fall. (I've got plenty of dried mushrooms, more than I'll probably use this year, I just don't like how the mushroom's delicious flavor turns into a rancid-sock flavor upon drying)
From my own personal experience, I'm really skeptical of the claims that proper drying is crucial to using the mushroom. There's a 1993 paper by Tsunoda et al, entitled "Change in ibotenic acid and muscimol contents in Amanita muscaria during drying, storing or cooking," (Journal of the Food Hygenic Society of Japan 34(2): 153-160) that I really want to track down to find out what it has to say on the subject.