Best New sports car buy assuming most, if not all, criteria listed in post #1 are met - I am going to ignore the luggage criteria so forgive me this transgression - you can buy a $5,000 used Camry along with the sportscar to handle the mundane activities:
Under $20K: Mazda Miata base - great handling, good car to track with
Under $30K: Base Evo or WRX STi - fantastic price/$
Under $50K: Corvette coupe
Under $100K: C6 Z06 for the performance fiends and 997 C4S for the all-weather all performance
Under $200K: F430 - if you can find one at this price
Price no limit: Pagani Zonda F
Anticipating the future thread of best used car buy:
Under $20K: E30 M3 or E36 M3
Under $30K: Corvette Z06 for the speed crazy or for those who would like to experience classic cars: Late 80s Porsche 911 Carrera or 930 turbo if you can manage it - wont be that fast but they are true driver's cars
Under $50K: Corvette Z06 for the same reason as above .. or .. Ferrari 348/Porsche 993 Carrera if owning a car from these two marques is a childhood dream
Under $100K: Porsche GT3 for track work; Prosche 911 turbo for the road; Ferrari 355 for the sound/involvement. Can get a very early Modena but might be dicey purchase
Under $200K: Challenge Stradale - Ferrari's greatest car in 20 years
Price no limit: 1. Ferrari 288 GTO - my all time favorite 2. Mclaren F1 assuming you have your own private circuit - Mas Du Clos for instance
3. F40.