Too many MKII TT's!!!....get out of here, the MKII TT is still pretty rare, I'm tripping over Z4's and Boxsters though, everywhere. The Z4 is an awesome car, but far more ubiquitous than the MKII TT.
When the Z3 came out at first, it received rave reviews, until the MKI TT arrived in 1999 and killed it. Then, I admit, the Z4 came along and made the MKI TT look rubbish (but the MKI TT had been around for 4-5 years by that stage and every car has its day, even an iconic car and I could post pictures of a Z3 here that would make the MKI TT look like a Lambo Gallardo).
Then in 2006 the MKII TT raised the bar considerably again - aluminium/steel hydrid, magnetic ride, best BHP/wt ratio in the class and up-dated more aggressive looks. That's why I changed and I honestly haven't looked back....that's why BMW will be bringing out the new Z4 possibly in 2010, and I bet you the first thing they do is test it on the Nurburgring against a new MKII TT...to keep the game going, they keep out doing each other every 2-3 years.
P.S By the way, SLK 350....Very nice motor.
P.P.S You mentioned the Z4M....its 10K more than the V6 MKIITT so not comparable. The V6MKII TT competes with the 3.0Z4 only, both the same price. Audi is bringing out an RS-TT in 2009....possibly 350hp.....that will be the Z4M'sc ompetitor. And the new TT-S available in Aug 08 will be interesting...272hp, 0-60 5.2sec....but, I wouldn't want it....2.0 4 pot turbo charged to within an inch of its life, I prefer linear V6 power, still the TT-S will be very interesting.