I think the training that helps with nuggets is worth getting too, especially when we start playing with mythril and gold. But maybe it's not a priority. I can't comment on the stat things.
I've noticed that the number of marks you get seems related to the rank of the leve in the same way battle leves are. I just got 1270 for handing in a rank 35 leve. I get so many 450-750 mark leves (in the rare times I get marks) and they're probably from 20 and 25 leves.
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