Well - this game could certainly use some extra features that could allow you to spend excessive coins and seeds.
For example that Garden thing thats on DMM, something similar where you could purchase the items displayed for coins and different sceneries for seeds. There would be NO option to use real money for this, as the only purpose of this would be to get rid of the excess in your inventory.

Another pretty good idea if I may say so myself, would be to implement a Slot Machine of a sort. Each spin 2000 gold/1000 seeds for eg., with some chances of getting lvl100 stuff like Bloom Dragons, Manyus, Ampys, Flower Gems, Crystals and all types of Skill Blooms. The usual "Line up 3" slot.
Similar concept was implemented in Borderlands 2, where mid game+ you DROWNED in cash. This was a great way to get rid of it with a hope of getting some rare High Tier equipment, new skins for your class, or Crystals used to upgrade your weapons. This concept would work well for FKG as well, and would allow high level players who have tons off coins and seeds, to spend it on something more useful, or just spend it for the heck of it.
(now the reason why the slot would not include any characters is simple - it would go against the whole "gacha" system, because "omg giving stuff for free" - which would not be correct btw, but lets not get to deep into that one, thats why I excluded those from the spins).
With all that said though - this is a browser game, which already puts a solid limit on what can be done, never mind the second points - its backed up by a company that does not seems neither ambitious about its project, nor cares that much about its player base. So with regards to that I dont expect them doing anything about this excess situation at all.