Hi mate and welcome.
Z4 - you really need an Alpina or Z4M to compete with a Zed IMHO - the 3.0 is fast but a bit souless - and I think they'll be out of budget
TT - only buy this if you're turned on by quality interiors and fast cruising - no passion and no RWD
S2000 - still looks great IMHO 10 years on but I've always been put off by no torque
MX5 - don't buy this if you want respect from the general public - only those who know about cars will understand the sweet RWD handling, you might just about manage a mk3 and turbo charge it (Litchfield are the people to speak to) or you could FI a mk2.5 and have money to spare (and leave the MCS behind)
350Z - on your budget this would be my choice every day - tons of car for your money, great engine, great sound and tons of character - take it from someone who knows, these cars get under your skin