I bought the extended maintenance for my M5. Already has paid for itself for an oil change, 4 rotors, and 4 break pads.
It's kinda like paying for service up front, though some maintenance items (like brakes) are above and beyond what the extended maintenance cost is.
So unless you are a DIY kind of guy and know you way around parts and maintenance, then I say go for it. Other alternative is to find a BMW mechanic that does work on the side for cheap.
'06 BMW E46 ///
: '08 BMW E60 DINAN ///
M5, Interlagos Blue, SMG
DINAN Stage 2 Suspension, Exhaust, Stage III Software, Front strut braces,
Intakes, 13% Underdrive pulley, 3.91 Differential, RPI Scoops.