Is GWE: Change for Psi damage worth it?

I have the others in that set. Does it give the chance to all my powers or just the hold? I'm not sure about giving up a perfectly good 53 SO Hold for a 20% chance to do minor damage (and some minore resistance to Psi). Please advice.

Just the hold. I mainly use HOs in my single-target holds anyway to add some damage.

Not much. I only have unique one in Tempest (chace of end drain) but never see it work or didn't realized tbh.

As Okton said unique damage enhancement only give extra damage to the power you slotted.

As resistances by sets, sorry but I don't feel any difference due to sets i placed. (Placed sets are Hibernation 5, Nightmare 6, Malaise Ill 4, Ruin 3, Harm.Healing 4, Touch of Death 4, Preplex 2, Temp.Readiness 5, Tempest 4) Maybe it is because of the sets i choose. Anyway i still got sets to put in some powers.

It's not unique.

Persoanlly I think Damage procs are very worth it in AoE powers (more targets means more damage), espcially those that cause aggro but no damage in the first place.

Grav and Ice Control are especially good for this, as their powers also cause Slow which means you have twice as many procs to choose from (hint: choose both!).

Damage Procs tend to more worthwhile the more of them you have, so slotting in multiple powers, especially powers with faster recharge, works best. As such, Recharge set bonuses (or LotG: Recharge) are mighty handy too!

Of course all this comes at the expense of slots elsewhere, but lvl 50 IOs and set bonuses help counter that loss quite nicely.

I've GWE in my Gravs single-target hold, just as an experiment. It'd work much better in my AOE hold I think along with as many Acc/Recharge/Hold & Recharge/Hold IOs as needed (I've gone for 60%ish accuracy and as high as possible for Hold & Recharge).

Damage Procs shine in AOE immobs since they are so quick to recharge. My Crushing Field now has the Immob Lethal Damage proc, the Slow Smashing Damage one and the Targetted AOE NRG Damage one along with a pair of Accuracy/End IOs making it a fairly lethal power on teams, everything hit has about a 50% chance of being hit by at least one of them. And it sets up containment for a follow-up fireball.

I've just put the Slow one into Oil Slick Arrow too as it'll do a few "ticks" of damage to everyone in it. AOE is really the way to go with them.

Try and get the Procs from the lower levels if possible as they use slightly less expensive Salvage. The Slow one in the level 20s uses fairly cheap salvage.

Correction:

After these talks i examined a little my Levitate, which i add the Chance of End drain one. It usually works. If i have to give a number, it is 3 to 1. I mean for every 3 attack one of them drain endurance from my target.

I thought the normal proc ratio is 20% ie. one out of five? At least the one proc damage IO that I have on my stalker seems to follow that curve.

I think damage procs tend to follow a general 20% trend.

There seems to be bit more variance through different effect procs though. Chance For Build Up is 5%. If I can think about what I have, for one, I think I have a %chance to stun on an immob' that procs around 2%.

Perhaps status effect procs or buff type procs generally trigger at a lower %.

Damage procs are nice, but it's worth considering if it slotting it comes at the expense of slotting more consistent or reliable damage, or even perhaps the chance to boost recharge from set bonuses, which might in turn grant another attack in place, which is always better .