I'm a bit confused here. From what I have read here in the forums, some time ago everyone thought that crits don't depend on DEX but only LUC. Then, when you got to the lvl 50+ maps (especially Pando), it turned out that this isn't correct, DEX has an effect. It is still a secret how the crit rate formula works, but having a bit DEX when you are at lvl 50 has been proven to be the right thing.
But now you suggest lvl 5 shrewd even for a lvl 30 build?
I guess you will answer that you need that DEX to hit other high-DEX chars in PvP. Has it really been proven that DEX helps at low levels or are you only blaming a Usual Subject? Even if there is an effect, other ppl won't have so much DEX as the mobs at the high level maps, they will have only enough to hit in PvP but not more (or they will sacrifice some STR).
To make my point clear: I am not suggesting to leave the spot where you would put your Shrewd unlapised.
But adding Craft instead would increase you crit damage as well, Life would add some survivability (more than the increased evasion from DEX I think), you could add another Dual Fortune (one with STR, one with Resist, maybe one with some more SP could help) as well.