I'm with Mike on this one...I'm sure 4 of the same lamp is enough anyway. They haven't been made in years too and I would guess a lot of people here don't have one.
as long as they're put to good use there's no harm. since you have fixtures go for it! I was referring to some people who like to hoard vintage things and resell them.
I'm kinda on the fence about people buying a lot on eBay if you don't have a use for them since it deprives others who might want one of them.