I don't think the powerful critical is that important. It will make a big difference in your hunt as you do more damage which will mean more life/mana leach. But other than a quality of life improvement I don't think it is going to open up any new spawns that weren't available to you before. It would increase your profit slightly in the long run though.
Before I run a few calculations I would like to make a note that you can get the powerful strike, void, and vamperism from the heart of destruction quest. It is easier to do void and vamperism from the 2 Forgotten Knowledge bosses, but it is definitely easier to finish Heart of Destruction for powerful crit than to do the final boss of the Forgotten Knowledge quest.
Now for some math. The difference between intricate and powerful crit is 25% (25% vs 50%) which seems like a lot. But it is only on 10% of your attacks. So if you were to do 10,000 attacks only 1000 of them would be crits (statistically).
So 9000 regular attacks at 500 damage would be 4,500,000 damage.
1000 Crits at 25% extra damage on 500 damage would be 625,000 damage (1000x500x1.25)
1000 Crits at 50% extra damage on 500 damage would be 750,000 damage (1000x500x1.5)
The 25% extra damage only gives you 125,000 more damage on 10,000 attacks.
This of course is only on single target, if you were to say these were exori hits and you were hitting 8 enemies every single time we could multiply the above values by 8.
750,000x8 = 6,000,000 and 625,000x8 = 5,000,000 which would give you an additional 1,000,000 damage over 10,000 exoris. So on average 100 more damage per exori with the above assumptions.
Someone can feel free to correct my math if I made any incorrect assumptions or calculations but I guess you can look at the numbers and draw your conclusion of how important it is.