First of all, how are people supposed to test a warpcore, if they have got only a white version? We need a Testitem-Vendor, if you want us to test the amazing abilities they should have.
There is currently no possibility to craft a warpcore or buy one of rare or very-rare quality.
From what I've seen a warpcore allows you to have a powerlevel of 130 to one subsystem, since everything is just DPS-related (I mean the whole Endgame-Content) you could give us only the one version that allows us to have more weapon-power (and a non-Escort would have trouble to get that powerlevel)
There is no ship, that offers you +20 engine-powerlevel or +20 shield-powerlevel, while there are escorts that have +15 weapon-power, there is an assimilated console that grants you +5 weapon-power and there are just a few skillpoints you need to spend to hit +25 weapon-power. The only exception to this might be the Vesta with its Aux-DHCs and a maximum of +15 power to auxilary.
The uncommon bonus is 7.5% Bonuspower from one Subsystem to another, so for every ship out there (except for the Vesta again) it will need to be Weapons to Engines, Weapons to Auxilary or Weapons to Shields.
So the whole Warpcore is just designed to give Escorts more directed energy firepower and a bonus to shields (for regeneration and the powerlevel-based resistance) or engines (higher defense-value and turnrate) - welcome to Escorts-Online.
If Star Trek Online was an Open-Source (GPL) Game, we would have a low-grind fork.