M Sport Plus = 19" wheels, privacy glass and HK audio. The heated seats are standard, as are xenons. I am talking about my 2015 model but, as was said above, you could get a facelift for your budget. I got an M Sport Plus model because I desperately wanted HK audio. The black windows are OK and wheels look nice but they were not my main reasons.
As far as BT, mine does not have Enhanced but I can stream audio from my iPhone with no issues. I can use iDrive to search through music and podcasts etc. I normally plug it into a charging lead from the central cubby to get better quality over USB and keep it topped up if TomTom running.
Extras I have:
1) Folding dimming mirrors. Excellent for not getting dazzled by Range Rovers etc. on the motorway. Also handy, after parking such a wide car to be able to fold them out of harms way.
2) Pro Sat Nav. I'll be honest, the frequent map updates, speed camera database and fantastic traffic info on my TomTom (iphone) way outstrips what BMW offers. However, you get a big screen that can run in split screen mode, no bits of 'poverty plastic' each side, a 20GB HDD for music and maybe more
3) Lumbar support. My only other extra and it's a waste of time as I have set it all the way down and part way out, i.e. just like the seats on a non lumbar equipped car!
Extras I wish I had:
1) Reverse camera or, better, surround camera. It's a massive beast when parking etc. and these would really help.
2) Comfort access: The system is half keyless in any event but it would stop me getting the key from my pocket only to put it back there again.
3) Memory seats if my wife drove it. She probably never will so no biggie ...
4) Some of the extended packs as I only realised after I bought it that some tiny things that had been on my 10 year old 3 series were missing as they are now in packs: Max cold button in extended aircon, curry hooks in extended storage, probably with the missing umbrella holder, puddle lights in extended lighting ...
I love the car. My only complaints are that it's huge (can't blame the car for that) and a bit less economical than I thought it would be. I'm averaging 44mpg and I do mainly long trips and drive like Miss Daisy. Every trip I do, I think if it had been 3mpg more, it's what I would have expected.
Overall, I loive the car and it drives and feels just right for what I want: An executive family estate with good boot capacity. Wish owner 1 had ticked some sort of camera but hey ho.
Edit: Forgot to answer your point about 530d/535d. Certainly they will be a smoother sounding and quicker so ask yourself carefully what you really want. I have an Elise 111R in the garage (revs to neaarly 9000rpm :)) which occasionally goes on the right roads at the right times for a damn good blast. The rest of the time, on more crowded roads, I basically toddle around at the speed limit, overtake if I really have to and listen to music. The 520d is actually pretty quick and I only use a fraction of it's performance. If you drive like me then fine. If you are always putting your foot down, burning people off at the lights etc., I'd say get one of the 6 cyl cars.