Jim,
I know what you mean - I'm 35 and have 15 cars since I got my license. Some of these include VT SS Commonwhore (modded), 200SX S14, RX7 S4, Swift GTI, VN 5.0L efi, VH SLE V8, Prelude, etc etc.
The Skyline is by far, the best, most fun, unreal, car I have ever had. As you said, I would only change it for a GTR.
Bring on the Lines - I'm hooked !!!!!!