Tracking Implants?
While it is technically a level 4 rare technology gated behind another rare technology, at least the predecessor technology feels like I draw it "all the time".
Subnormal Stimulation is only tier 2, has nearly twice the base draw rate, has a 1.25x modifier for being not egalitarian (aka most empires). It's also a rare technology, meaning if you took technological ascendency (like most players) you get a further boost. And then finally there is a bit of observation bias going on, since you see a shiny rare tech and get excited, then see what it is and how it's useless, and get sad, so you remember it more than when you draw the level 2 +30 naval cap tech.
But the key thing there is you
draw it all the time. Not research. Unless you are proactively paranoid about espionage, or are at the end of the tech tree, you won't have any reason to grab Subnormal Stimulation or Tracking Implants ahead of time. Far better to get techs that improve your economy, research, or military. But if you are suddenly beset by espionage, you then need to get lucky trying to roll both those technologies, which frankly won't happen in time to matter.
Aye, that was my idea: to make the intelligence edict a costly, albeit powerful common tool for all empires, gated only by a regular technology requirement. I dig the idea of an edict that makes your empire go into "bunker mode" regarding spy incursions. The whole "accumulating spy bonuses via several edicts" is far less attractive to me, especially if those edicts have the same drawbacks (happiness penalty). I would much rather distribute encryption bonuses through other methods (Traditions, diplomatic instances, etc).
I do think there should be a few more encryption bonuses scattered around. And it's less "accumulating spy bonuses via several edicts", and more that I don't think going past +4 encryption on a single edict is very balanced, but there is a sliding scale of how much encryption you need in order to shut down spy networks. Against an equivalent empire (at least in terms of Codebreaking vs Encryption), a single one of these edicts will shut them down (Technically it is always possible to spy on someone*) For an empire focused on espionage though, you need multiple. I do think that's a good thing: If an empire has significantly invested into pursuing espionage, it shouldn't be as easy to shut them out as it is for a normal empire.
You do have a point about the same drawback, it can be things other than -10% happiness. So for example you could have an edict "Diplomatic screening" reducing empire relations and increasing diplomatic influence cost in exchange for that +4 encryption. But for the three existing edicts, I'm struggling to think of a good penalty besides the -10% happiness. Maybe Enhanced surveillance could give +25% empire size from pops, but I don't think that's as punishing as -10% happiness.
Thinking about it, I actually kind of want to not put an encryption edict in technology, or at least not a very strong one. Espionage is one of the aspects of the game that makes sense to be heavily focused on society and culture rather than just technology, and it could be a way for an empire behind in tech to still punch up. So an empire which beelines technology but discards unity should be weak to espionage. That diplomatic edict would git in Diplomacy, maybe something for adaptability or harmony? Not all of them need to be edicts, but I do think there should be a spread of "turtle up" edicts.
*Encryption caps at +4, giving -40 maximum infiltration (10). You can use gather intel operation, which only needs 10 infiltration, to get +5 max infiltration, up to +20. With 30 infiltration you can acquire assets like normal to increase it further. If an espionage network already has assets, then max infiltration is less of an issue, just hire more assets. But what IS an issue is the difficulty of operations: +4 encryption also gives +4 operation difficulty. While an operation will always progress at least one stage on a roll of 10, I can say from experience this takes FOREVER. An empire who is already established and has the perfect assets for the operations they want to run will have a much easier time though, to the point where I think there needs to be some anti-asset mechanic in play. Or maybe the turtle up edicts just need to increase operation cost, so even if you do have the encryption to push through it's more expensive.