The performance you have with the 370 is going to be hard to match at that price point, so like you say, GTR, R8 kind of budget.
Do you want to be busy with another project? Now i know you are a man that likes to "tinker", but 1700 miles is still time driving, not hidden away in the Shed creating and you are coming into that time of year when enjoying cars comes to the fore (spring/summer), so maybe you will do more miles this year in the 370 or GTR/R8 etc as other projects have been completed?
The track work is taken care of so is a sports/supercar really the route, i.e does it really need to be edge of seat type drive or, something way more GT that you will maybe enjoy driving some as its no so on the edge, bit of luxury, comfort and all the goodies but still lifts up its skirt should you require.
So what am i thinking, maybe Maser GranTourismo, AMG something, Aston etc
If you really must have ANOTHER project, do the pick up, cheap, cheerful and will allow for the being stuck in the Shed with you're creative juices flowing, but still allows for a nice motor to enjoy when takes the mood!