
A little background:
I bought my 57 plate Z4 back at the start of 2013. You can see her above, resplendent in the sunlight. I needed to replace my rapidly declining E46 320d and a nice straight-six 3.0 seemed like the obvious next step

Sadly, she proved a bit too expensive for me, so I resolved to sell up for something more sensible. I part-ex'd her for a 120d, which became the source of a living nightmare for me. If you want to read the whole miserable affair, you can do so here: http://blog.edhirst.com/2013/11/13/bmw-timing-chains-and-used-car-dealers/
An exploded engine, a faulty replacement, and endless amounts of cash later, I got shot of the car, and am now tooling around in a 53 plate Ford Focus 1.8 Zetec. After owning BMWs for 6 years it's come as a bit of an upset! Though I am glad of having SOME transportation.
Thankfully I picked up a much more lucrative job at the end of 2013. Ironically I could easily have afforded to keep the Z4. I'm saddled with some debt, thanks in no small part to the legal wranglings involved in the above link, but those should be done with soon.
The new job means I commute into London via feet / train, so my annual mileage has dropped way down to about 6000. My circumstances almost make a Z4 even more perfect - the odd evening drive and then fun on the weekends.
Come the start of 2015 I'm looking forward to a 10% bonus, plus hopefully a promotion and all the goodies that come with it. I'm going to use the bonus as the starting point for a new car. But I find myself with a terrible, first-world-problem dilemma

What to have?
I loved my Z4. I think the styling is fantastic, it went like a rocket and I've never loved a car so much in my life. I'm tempted to get another of the same shape (or the hard top, which to my eye is the more beautiful of the two), but they are getting on a bit now, and I'm concerned that it won't see out a 5 year period in the cheapest way possible.
The other choice is to look at one of the new Z4s. Once more, beautiful styling although the move to a more 'GT' type of car is a bit of a shame, I think. The problem here is that I could never afford a brand new one with the levels of kit I'm eyeing, along with the engine. So I either get a big fun motor and few toys, or the other way around.
Is there any point in having a Z4 with a 2l motor?
Buying second hand is another option - though they are more expensive, and I'd be worried about the servicing costs.
The last option is the one that seems the most sensible. A brand new 3 series. A frugal but punchy turbo'd diesel or petrol motor with a decent level of spec, plus BMW look after all of the servicing etc., if you buy the packs. It's a lovely car, good looking, and will be more practical, should I ever need practicality.
The 3 series seems like the obvious, safe, reasonable choice. But ... not the fun, Z4 shaped one ...
What would you do?