Yes, there are some weapons that have special properties. Evicous has a topic listing them here
. I would post it again, but it is a little long.
In terms of super rare items there are a few. Psycho Wand tends to have that reputation and I think Clair Doubles is considering very rare as well. Other than that I can think of the Missouri weapons, the shurikens (Fuuma and Kouga) and maybe Al Azif. Psycho Wand is the big one though and it seems like very few people around here have it.
As far as I know the DS is not region locked. I know of others playing Japanese versions of PSZ and other games without a problem.