E9X or E46 M3 cabrio.... It was certainly a tough choice for me, so I bought both!
But seriously, why are you comparing apples and oranges?! Each car has its own purpose in its own respect. And not to mention you're comparing brand new car vs. used car. Why would anyone buy new these days? If thats the case, why not buy a new E92/E93 M3?
One is a coupe, other one is a cabriolet. One is 100% track ready, other one needs an LSD, and some suspension/brake mods.
Is this going to be your only car? how often are you going to drive it (i.e. Weekend car only or Daily driver)? Is this your first BMW?
Keep in mind, an E46 Waterpump alone is $600-800+ just for the part! Are you financially comfortable to make this car your daily driver considering BMW puts a premium on every M replacement part?!
Also keep in mind, you buy a 3.0L Biturbo car, you're obviously going JB3+ chip or similar ECU tune. And ofcourse as soon as you start boosting more and more, thats reduced turbo life drastically, and eventually you'll have to do costly turbo replacement maintenance on your daily driver. Are you able to justify the cost of replacing turbo's on your daily driver?