If you have a bit of diy nowse and some tools you can change the breather yourself. It was a 'Hot Topic' a few months back so a search of this site should come up with a series of results and piccies. It will cost you less than £150 too. It's not a difficult job, but it does need some disassembly and several of us have done it successfully. It's a good idea to change the air filter too.
Pano roofs are indeed a problem, and the rear section particularly. A fair number of people have has complete replacements fitted. To get at the rear motor, it is necessary to take the headlining down, so £200 does not surprise me.
BMW can be a bit 'sniffy' about anything that they don't fit themselves. Tyres are something that a number of manufacturers are careful about as 'technically' the tyres in use should only be the types that the manufacturers homologate their vehicles with. That doesn't mean that out of warranty you are forced to only use 'OEM Approved' tyres, just that the manufacturer would prefer you to use only the 'right' ones. You are completely at liberty to ignore them
