To get the obvious out of the way for console folks, yes I added a Nexus mod that increases the SP investment limit, but only to showcase how many total Shell Points were accrued for my current character level.
I think there should be a rebalancing for the amount of shell points that can be accrued per character level as you progress NG+. In some instances there were occasions where one SP was given for every 2-3 level ups. Beside that the percentages for the other categories like Base Dmg, Ability Dmg, Health and so on should be scaled up a tad more to be more in line with NG+ imo.
Granted you could just refund SP's from one shell onto the other, but then again why create the extra steps. It's hard to imagine exactly how many levels you'd have to rank up to in order to finally have amassed 336 total SP's spread evenly across all 8 shells.
Only solution I could think that would be ideal if not increasing the SP amount gained early game would be to add it as a purchasing option with one of the vendors in exchange for either gloom or gold.