To be honest if I where still on my Ps and wanted a Skyline for around $15k (which what looks like you are) I'd look for something like this.
For those too lazy to click the link it's a V35 Skyline 350GT-8 sedan.
Yes, it looks like a bucket of aids (imo lol)
Yes, it has 4 doors
Yes, it has a CVT trannie with flappy paddles
Yes, it doesn't have the street rep like the R chassis Skylines do.
But here are some things to consider
Stock for stock a VQ35DE puts just as much, if not more power out as a RB25DET, let alone a RB25DE
A VQ35DE burns less fuel than a RB25DET
It is a newer car, newer cars have less age related problems
Because it doesn't have the street rep, people won't notice it as much. This includes police and thieves
Being a newer model, it will probably hold its value better (though I'm no fortune teller lol)
At the end of the day the final decision is yours, but I tell you now, consider what you are going to do with your car when you get off your Ps. I'd be surprised if you kept it naturally aspirated instead of selling it or dropping a turbo engine into it.