You don't need Dexterity to critical, critical hits always
hit! Dexterity only helps you to hit things when you do normal hits.
The only reason I bother to put any points into Dex at all is because it boosts your SP. I tried making a pure Luck build (all points in Luck) which was very, very good, but I found that I was running out of SP too quickly.
As for the boost to evasion that Dex gives, it's not really needed, but it's nice to have
So the 1 Dex, 4 Luck Build really is the best.