I love how investing into Portal Guardian talent actually spawns visible guardians around your portal. The visual upgrade gives me as much of a sense of improvement as the actual effect of said talent itself.
It really makes me hope you find the muse and time to add similar effects to other talents so that our traps and cores look as badass as they are in late game.

Additionally, some of the talents like linkage or singularity could benefit from visual feedback which makes it easier to tell they're active (you'll notice in my examples).
I mean, to employ an hyperbole: paralysis is practically indistinguishable from a hic-up in pathfinding.


Particular suggestions:

Linkage
Actually connect affected traps with glowing chains. I know there isn't a lot of space and your resolution isn't too forgiving but perhaps you could make them appear to hang out at the sides for vertical connections or top/ bottom for horizontal?
The more adjacency bonus, the more chains there are or the brighter they glow.

Bribery
Add heaps of gold coins and diamonds, and partially open treasure chests in the four corners of the portal.
Empty the chests while player is below the minimum treshold (talent is inactive).

Singularity
Add a blue, swirling vapor that loops over those traps which meet the condition (only 1 of it's type). Don't forget infinity loops unique item allows you to have several Singularity traps.

Overload (Brute tree ultimate)
Add a glare which seems to break through the openings and gaps of affected traps from it's core to the outside. That baby is in maximum overdrive! It's about to blow!! :D

Loophole
Place the actual portal from the picture infront of every core which has it ready. Portal closes / disappears while on cooldown.

Hoard
While above the treshold (talent is active), add an animation that makes it look like traps eject shells like a machine gun when firing. Except instead of shells they will eject coins.

Looting
Every 10th enemy (the one affected) bursts into a rain of gold coins alongside the vicera. There already is a similar special effect for nobles.

Paralysis
Affected enemies have yellow lightning arc over the surface of their body.

Scorch
Flames turn blue when entering their extended duration.

Deconstruction
Add a special, more beefed up sound effect to selling.