Interesting topic...
I've looked at Group C... but if something goes wrong and you shunt it at pace, it's often not survivable. Still tempted though of course that boat seems spectacularly missed now.
I too looked closed at 996 GT2 R's and RS's and RSR's... but running costs on those are daft and I don't think for everyday playing they'd work out significantly quicker than a later cup car... say 997 Cup? Which I prefer the look of and I reckon would be MUCH cheaper to run. So if I was going to buy a track toy, I think that would be the option.
HOWEVER, I too am much more persuaded by the older cars, for my mythical 100k, I'd get a fully race/rally prepped ST replica and run that in Classic events across Europe and have enough left over for a few entries and tyres etc!
Like the slightly left-field Cayman R suggestion... but can see them being the 968 Clubsport in 20yrs time... great car but still unappreciated.
I've got a few cars in the stable at the moment, and to be honest, the most thrilling is the one with the least power (130bhp) but weighs sub 700kg, has a close ratio box, revs to 7k and sounds like a sawn-off Lambo. After that everything else feels like u r driving around with the handbrake on literally.
Cheers
Rick