Interesting... although your downgrading from the top to the middle range skyline, and your worried about it having big shoes to fill... in some ways the WRX might give you that feeling abit more. I say so because the WRX will be an AWD, turbo car. And therefore you will probably be able to draw more inferences with the handling/performance of the car. However jumping back to a RWD 34, although its no GTR, it will provide you with a driving experience totally different to that of the GTR. The tail will be jumping out, power on oversteer etc.
To me, the WRX might make you miss the GTR more, because you will feel just how good the AWD of the GTR is when compared with competitors. However, the GTT will just form a tail happy, totally different drive.
Something to consider anyway