Percentage increase > Additive increase. At the current gear level, there's really nothing that beats Expertise because it has such a soft DR curve. If you could get to like 2000+ Expertise you'd probably be better of going Power, but as it stands, the difference between 1200 Expertise and 1300 Expertise is ~2% damage on all abilities, whereas 100 Power gets you +23 damage on all attacks.
So if your attack does 2500 damage on a standard hit, then:
2500 x 1.02 = 2550
2500 + 23 = 2532
So even at higher than 1200, still worth it. Additive increases are better for small damage numbers like DoTs, percentage increases are better for high damage numbers like your class' big hitter (Railshot, Back Blast, Death Field, Heat Seeker Missile, etc.).
That's how I look at it, but obviously you need a decent starting point for the percentage increase to be worth it, but even with 1300+ expertise you have plenty of room to stack Power to get your base damage high up there.
Power isn't simply additive. Each ability has a proper formula which uses the Total power for said attack type which includes Mainstat, Power, Tech/Force Power or Weapon damage (I will oftenly use the terms of Total power
with this as a defenition). If an ability has a formula that says that the damage are 2 x Total power
, increasing +23 damage in the Total power will give +46 on the said ability. An other ability could have only a 1.3 ratio, increasing its own damge of only +30.
In fact, what should be compared is not how much damage it adds on the statsheet, but how much percentage of Total power
you gain from Power. If you're a tank, with low Total power
, adding 100 Power *can
* imply a percentage bonus higher than the said 2% Expertise gives... I said can
because I'm not aware of how much it represents. But the more you already have Total power for exemple as a healer who has much main stat and much power, the less likely putting some Power will help better than expertise. But you also have to take in account the fact that it doesn't increase suvivability like Expertise does, so Power has to give a damn big bonus in order to be better than Expertise.