Would be a waste of money upgrading the amp and not the HU or speakers Pete
Is it really worth worrying about the factory BT? Yes you lose the steering wheel function but all I need to do to answer a call is press a button on the touchscreen? I could understand if you were a rep travelling 1,000s of miles a week but do you really get that many calls on the move
Yes:)
HU change, then speakers and amp
There's a thread somewhere on My350 saying they've had good results from just changing the speakers (maybe the amp as well, can't remember). I may be tempted to do that at some point as I can't stand after market HU fitments, they never look OEM enough.
Yeah you can get a better sound from changing speakers or speakers and amp certainly
Cheapest option would be a nice pair of comp speakers for the doors and turn down the rears or of course change all 4