Can see your logic straying away from a 996 Jackzi. Have you considered the M3's bigger brother, the M5? I've had e39 M5s for the past 7 years and they are a great 'do it all' car.
If your budget is £15-19k as mentioned in OP you'll pick up a very nice, enthusiast owned one that's had all the major jobs done (there aren't any really - bit of rust, brake line replacement). The 5-series is a big step up in quality over the 3-series too, and the e39 interior is one of the best.
Assuming you're happy to be in a 20 year old car (a la 996), if not and you're bit braver the later e60 M5 (v10) is in that budget range but is much more expensive to run.
If your budget is £15-19k as mentioned in OP you'll pick up a very nice, enthusiast owned one that's had all the major jobs done (there aren't any really - bit of rust, brake line replacement). The 5-series is a big step up in quality over the 3-series too, and the e39 interior is one of the best.
Assuming you're happy to be in a 20 year old car (a la 996), if not and you're bit braver the later e60 M5 (v10) is in that budget range but is much more expensive to run.