Is there any use for them other than at the memorial? Just curious.

Only if you have use for them in a treasure chest or gallery.

I'm planning to add mine to a gardening-themed shop :)

i'm waiting to see if they add any more tiers to the achievement this year; if not, i've got a huge stockpile ready to frag.

i always frag mine!

I'm saving mine for quests and the recycle beast

I've started throwing them in my gallery just in case.