3.0i is definitely worth it over 2.5i. I commute 36 miles a day at the moment - without hanging about too much - and I still return 32mpg. Insurance, if you're young like me, could be about £300 more per year, though.
The link Booner gave you is very good, but from personal experience watch out for:
- roof motors (as mentioned. A fully comp warranty with no excess will be £530 a year, ish. With a £250 excess it's about £320. I plumped for the excess option and have claimed twice so far
)
- springs (prone to going, similarly to the e46 of the time?)
- twitchy steering (usually solved by replacing runflats with normal tyres and having an alignment done)
- airbag light coming on (another common issue that I had recently. It can be a few quid to turn it off/replace the sensor, or you might need the entire control unit replacing like me)
- corrosion on double spoke 108 style wheels (basically, you'll need them refurbed every 12/18 months or you'll need to get a different set. Get original M ones like mine - they're great and fit no problem)
- seatbelts not returning (another BMW favourite, it seems. Easily solved by cleaning the extreme end of the belt and lubricating it with some silicone stuff from Halfords)
Just make sure servicing has been done on time. I wouldn't touch anything that has seen any action with anyone who isn't a main dealer or a reputable specialist. I've got an entire folder of past work to go with mine which I'll be using as a selling point at some point after July!
Any questions, feel free to ask.
(edit, in terms of optional extras):
- wind deflector. Vital.
- heated seats. Again, essential, if you ask me.
- uprated stereo. I
think there are 3 levels of it (and I believe I have the middle one with 6 speakers). The bottom one sounds a bit tinny, by all accounts. Mine's stonking, no complaints.
- cruise. Vital, in my opinion.
- xenons. Again, vital. The halogens are cack.
- sports seats. Nice, but you won't find them on the older ones. A few people on Z4F have retrofitted from breakers and it's something I've considered.