Hi all, just wondering if Crystallised Omniscience really is worth the high price to pierce monsters' elemental resistance?

That depends: you are most likely only able to play with a wand, where a staff build would be much more efficient to hit the deeper levels of penetration and do real damage.

Worked for me, i bought the expensive necklace and got lots of penetration

you can penetrate without necklace but it can help get started