I think the mistake you're making here is disconnecting both players' preflop ranges from their postflop ranges. I don't think it's necessarily a bad 3-barrel, but that doesn't mean there are no flaws in your logic.

Firstly, when you open UTG pre-ante you have way fewer ace of spades or king of spades combos in your range than in later position – you basically can only have AJo+, AJs+ KQs and maybe KQo. So, right off the bat this is going to be a more difficult bluff to make in this spot than it would be if you were in the cutoff and villain were on the button.

Secondly, a lot of the things you're attributing to villain postflop – “some goofy hand that he's planning to float twice”, for example – are just not realistic. You need to think about why he might float twice with a goofy hand here – there's just no reason for it. Unless he's an absolutely crazy player, there's not really any line of logic you could follow that would lead him to have, say, T7hh here.

So, this leads me to analyse the ranges villain might call at each point in the hand. Preflop, with him being a 'weak reg' UTG+2 facing a UTG raise, his range is going to be very tight. He might even fold hands like AJo, KQo or 22-55 with so many players left to act and only 40bb effective. This means that when he calls this flop, he's mostly going to have strong-ish Ax hands, plus the occasional set that he didn't decide to raise, and some spade combos with maybe a very small number of floats with other middling pairs or, say, a suited broadway hearts combo with some backdoors.

I'm kind of on the fence about the turn, to be honest. On the one hand, I don't expect him to fold many Ax hands to a second barrel. On the other hand, I don't see him calling 3 barrels here with AJ or maybe AQ, since our range looks really strong when we 3barrel from UTG, so it might be a case of 2-barrelling and giving up being really unprofitable, but 3-barrelling being actually quite profitable. I think he's going to have the ace of spades a decent amount once we get to the river, but he's also going to have the jack or queen sometimes, and a set very occasionally, so its probably pretty close.

I think the 3-barrel is possibly profitable in pure terms, but the main message of this post is to point out the inconsistencies above, and also mention that I think 3-barrelling people for your whole stack at 40/80 is almost never necessary. I'd probably just c/f turn and move on.