Pipe-dreams aside, and sticking with the Lily mechanic, a small tweak I'd like to see is that abilities only consume one lily when activated. Could still make the effect stronger based on the number of lilies you have at the time, but it only consumes one.

Lilies should be obtained from all healing, not from using specific heals. e.g., you've healed xxxxx HP, gain a lily. Overheals don't count.