As a classic BMW lover myself i fully agree with Gaurav. I wanted to buy a 540i Japanese import first but realized that it would take me many trips to the Sharjah workshops myself to keep things economical for this type of cars. Where i come from in Europe we have more spareparts and knowledge available to keep these cars on the road and also the climate is less demanding. If you're not doing too many miles on a daily basis it might be worth taking the risk, but be fully aware that it might cost you another +15kAED the first year to get the car in the condition you want and to repair the critical things.
I went for a 2013 316i because the resale value is indeed very low, and it was well looked after.
A decent Japanese brand with more spare-parts availability will give you more ease of mind. Did you consider an Infiniti G37 ? It's japanese, and it's fast. Not sure about the reliability though but my colleague drives infiniti and is really happy with it.
Good luck.