Alan Watts put it best: "When you get the message, hang up the phone." Respect the experience, the power of the drug, and know when to stop.
You may not unlock the secrets to the universe, but I do think it teaches you an important lesson that your reality and experiences are subjective. I don't mean that reality itself is subjective, but our perceptions of it are. LSD will mess with your perceptions in really weird ways that can't really be described with words. Things like your perception of depth and age get thrown off completely.
I think it depends how you go into it.
20 years ago I did magic mushrooms for fun. I did some more recently to give up smoking.
With a more mature outlook you can gain some real insights into yourself and the nature of your consciousness during a trip. Or you can listen to some music and have some fun. I ended up starting to meditate as a side effect.
(You mention that you took a "plethora of other substances", that probably doesn't help you gain insights into yourself.)
Sam Harris has some very interesting stuff to say about non religious spirituality (and the overlaps between meditation and psychedelics).
It seems to me like it would be a good way to go, a good way to conquer the fear of the unknown after you die.
In a related experience, once when I was on a bender, I took 3 tabs of lsd, along with a whole plethora of other substances. I actually thought I was dead for a while, and strangely enough, I felt OK about it. I saw some pretty weird shit on that trip, it was the most mindblowing experience of my life, and not one I'm about to repeat in a hurry, it honestly wasn't that fun. Fear and Loathing in Las Vegas is not an instruction manual.
But then I sobered up. I really think that Hunter S Thompson was right: it's all bullshit. You're not connecting to another plane of existence or getting in touch with your ancestors. You're just fucked on drugs. Nothing wrong with that, but it's not spiritual.
He really nailed it in Fear and Loathing:
> All those pathetically eager acid freaks who thought they could buy Peace and Understanding for three bucks a hit. But their loss and failure is ours, too. What Leary took down with him was the central illusion of a whole life-style that he helped to create...a generation of permanent cripples, failed seekers, who never understood the essential old mystic fallacy of the Acid Culture: the desperate assumption that somebody-or at least some force-is tending the Light at the end of the tunnel.