I have just spent 3 weeks going to every dealer possible, i test, drove everything from a toyota auris hybrid (i was meant to be buying something cheap and cheerful) to a corvette C6 (to pricey at the moment for a really good one, but i will get one in the future). I wanted something around your budget that looked good but was cheaper to run the the Z.
What about the new Peugeot RCZ, that is really nice and the interior is lovely, they are on limited production so not that common, but prices are still a bit high still, but the running costs are good.
I would not touch another audi if someone paid me, had the old 3.2 dsg - £8k of repair bills later. A bit common as well.
SKip the M3, they have the wrong image personally, go for a Z4m over the M3, but they are not practical.
What about an Range rover sport, look good, shift like stink and out run most stuff in the wet (got totally hammered by one on a winters norming earlier in the year) but maybe a little pricey, did extended test drive in one of these, including offroad, it is amazing a car. If i had to swap to having one car, this would be my choice, practical for the dog, tip runs, shopping and has the speed.
What about an alfa, after weeks of test driving stuff, my only option was the spider which i bought, a bit slow, but i have other cars if i really want to zip about, my brief was something that looked good and most alfas do. They are pretty reliable these days, not sure they really have much in the power range you are looking for though. It might be worth a look, remaps good option on these to beef them up a bit.
The only thing i can say you will not find the perfect replacement, i spent ages and in the end gave up with the power side as there is nothing to compare to the 3lt or Ms beauty and power combo. Therefore went for looks alone and scarificed 3.8 secs of 0 - 60

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