Grinding the Arena(s) for Seeds

[Islandi]

I'm past the Normal Ending and I've started grinding in Ghalzabine and Secret arenas for seeds for the last day or 2.
However I found even the reward of 1,140 coins per round from Ghalzabine arena is low, considering per seed costs 150 coins (which converts to 7 seeds per round).

To increase even a character's single stat to above 1,200 points takes A LOT of seeds. I can imagine even hardcore players burnt out from "endless" repetitive grinding. (I assume max stat is 9,999 given the space is just about right for 4 digits)

Does anyone know of a better way to acquire arena coins and seeds?