Boss made their pedals in Japan from the early days to the late '80s, then they moved to China, Korea, and other cheaper places. So a MIJ Boss pedal is not at all "rare", but it is older--and some people believe the older ones sound better, so they pay more for them. But in all honesty, there is little if any real difference, and MIJ Boss pedals are all over Ebay all the time, so the dollar difference is minimal. There are a couple of exceptions, where Famous Guitarist X claimed their secret tone box was a certain MIJ pedal, so the raving fanboy guitarists will pay top dollar for that one. But
AFAIK the graphic EQ was never one of those collector-coveted ones. If anything, promoting it as an MIJ may help you sell it "at all", as opposed to not being able to unload it.