Yeah Vertigo, I think you need to research what parts are actually JDM. This car was set up due to the tastes of various previous drivers. Just because it has the JDM taillight doesn't mean everything is JDM. I think that is the stock 2.5RS Coupe spoiler, the midrise version. There is also a low rise spoiler that came with it that is also a stock option, I believe they normally came on the 4 door. I don't know a lot about the history of 1st generation Impreza's. The version 5 that Nigel was talking about appears to be the STI style spoiler that comes on most later model (2004 & up) USDM STIs. Its like a midrise flat deck spoiler, not a curved one like the 2 that we have. I think that the ones we have are probably USDM.
I wonder if we could take the lights from the other low rise spoiler and put them on the midrise spoiler you are using. I would think that they would be same. Another thing to consider, the car might look good with an STI OEM style spoiler. Something like the Version 5 STI spoiler that Nigel was talking about. I don't know if you need to buy an actual JDM part for that though, I think you can buy them from aftermarket manufacturers too, although I don't know what kind of quality you would get that way.