A 7-level rouge with SA deals 23.5 (1d8+4d6+5) damage on a normal hit. This increases to 42 (2d8+8d6+5) on a crit.
Advantage improves crit chance by 0.95*0.05=0.0475
Elven Accuracy improves crit chance by 0.95^2*0.05=0.045125
0.045125*(41-23.5)=0,8348125<1
Your average damage increase is less than +1 per shot from the crit chance increase.
You have to also factor in increased to hit chance. Average AC level 7 enemies that matter enough to bother with feat selection efficiency should be around 18-19 (ex. mean dragons and demons, Fire Giant).
It is also convenient for calculations to assume a base 50% hit chance (+5+3).
Advantage gives you 75% hit chance.
Feat gives you 87,5% hit chance or 12.5% increase.
Not going into the complex-ish calculations this should be slightly under +3 damage per shot with advantage.
Given the same assumption, your aDPR with advantage w/o the Feat is ~19,5.
TL:dr
For your character, assuming no other magical shenanigans, this Feat increases your aDPR by ~3.5 for attacks with advantage or by ~18%.
How does this compare to other options?
