I just went thru this last month; '07 3.0si with Adaptive drive(Electronic Dampening Control). "EDC malfunction" message started coming on intermittently at about 115-120K miles; then on all the time. Car drove like the struts were completely shot, since each shock's fluid valves default to the "open" position. Front AD struts are about $800ea, and rear about $500ea just for the shocks (thru "yourBMWparts.com"). No rears anywhere in the CONUS, and about a 2 month wait to get them from Germany... So, about $2800 wholesale just for parts. Then add $400 for an AD wheel alignment...

I'm getting ready to sell the vehicle; so, no way I was dropping $3300 on shock swap for a $6000 car... Especially after dropping $2500 earlier this year on other maintenance; (H2O pump, AC compressor, front crank seal, DISA valves, fluid leaks, etc)...

I ordered non AD Bilsteins for all 4 corners, new bumpers and cushions, and had to replace front springs since one had broken in the strut. Replaced them all without any issues. Will always get the "EDC Malf" on startup, but the car rides and handles much better. I don't believe it can be coded out, but frankly IDC...

As a note: the front and rear AD sway bars will not work as designed, since the AD system completely disables itself if any part is inoperative. The E60 series has standard struts with AD swaybars, and works fine, but the E70 is all tied together (according to the local BMW stealer).

Bilsteins: $670
Cushions, bumpers, and hardware: $130
Used springs: $125/pr
Total: less than $1000

If you plan on keeping the car long term, and go the standard shock route; you may want to consider replacing the AD swaybars (and mounts) with standard ones from a wrecked E70. It will also require plugging the hydraulic lines from the PS pump that supply fluid to the AD sway bars...

Good luck whichever path you take.