Ast cards should stack.

[JowyAtreides]

This is why I suggested lowered MP costs.
It would compliment Ewer thematically, fit with the 'more energy' symbolism of the Spire, would serve all jobs as TP is getting merged into MP, and it wouldn't be redundant to Ewer as one recovers MP while the other prevents it's loss. You'd use Ewer when you were low, and Spire when you weren't, or at the very least you wouldn't use it any less than the current Spire.

I hope this happens. Best idea I've seen yet.