Well, I have some news about parts availability for you from inside BMW Mal...
If you need a new, say, rear ESA unit on warranty, it is either available from BMW stock, or it is not.
It makes no difference if you have the warranty or not, the part is either available from stock or it isn't.
BMW dealers don't have a separate stock on which they can draw.
Having the warranty won't get you a part if it isn't available. It will, however, save you money if you need to invoke the warranty.
The issue is not availability, as you say, it is cost. But that is only relevant if you want new parts bolted onto your 'old' bike.
Personally, if the rear ESA unit goes on my late 2012 K13S, I neither need, nor want, a NEW ESA unit. A unit off a late model will do me fine, younger than my 'failed' unit but still working.
When my 2004 K12S ate its throttle bodies in late 2011, a set off a 2007 bike for £99 from James Sherlock was marginally better than a new set from my friendly dealer at £1,000, worked perfectly and as far as I know, still are!
If you can do the work and are happy with spares off a 'broken' bike, the warranty is expensive and the servicing even more so.
The other factor is whether your bike is a working tool or a toy,
Mine is a toy, if it is off the road I get a kick out of getting it back on the road. When my R1150GS was my commuter tool, it had to work, every day, all day; but then again, 1150's never went wrong
