IMO:
I would think for today's inserts, with many brick hunters offering them in UNC, there is a very small market for notes in circulated condition. That has been my experience so that I've spent 1 BEK, a few FER, 1 FEV, 3 BEV's, and many other inserts in less than VF condition. When the note is high grade I might keep it...but odd thing is ... most people I know still aren't satisfied with EF to AU! I would think you've gotta hold onto these a minimum of 3 years to see any increase in value, and then there's plenty of other notes people would rather invest in during that time. I often spend (or trade) lower grade inserts/radars at shows...but I've yet to see a dealer show any interest in them. The trades only go to other collectors.
I guess with the lower denominations-- they're easier to set aside and perhaps save for a trade. Unless you're suspicious of the prefix (being short, etc) I wouldn't be too keen to hold onto a note like that...but then again I may be wrong. There are few FEP inserts. Its probably worth hanging on for a later trade.