I recently purchased a '17 GT PP. The '18 was intriguing but the deal I got on my '17 paired with my preference on the looks sold me. If you do go with and '18, you may want to wait until next summer when you'll be able to get a better deal. Good luck!
Was it the whole car or just the hood? When I had an S197, I noticed my air deflector under the car came loose which caused a lot of hood vibration above 70mph. Upon properly re-securing to my car, the issue went away.
Just another thought...good luck!