Yeah, getting 255 Luck makes Evasion and Accuracy pretty obsolete. Accuracy can be abandoned and Evasion doesn't need to exceed 30. And there's no point in getting more than 170 Agility if you have a weapon with Pre-emptive Strike (and if needed switch weapons in the very first turn)

I've never bothered to build a perfect sphere grid. In fact, all I did till now was bringing all stats to 255 (except for Luck, it's somewhere in the 100's, I got bored farming the spheres) but keeping the +1/+2/+3 nodes and being happy with 9999 HP. Seriously, I don't think I'll ever need more than 9999 HP. Not maxing HP will save a hell lot of time as well.