I had some issues with my 08 X5 that seemed to be common issues.

Peeling steering wheel trim
Water in rear light housing
Loose rear bumper

I had all addressed as part of the cpo, but the bumper was a pain, and had they denied me, it would have been pricey to pay for a new bumper. There is a multi-page thread on it on xbimmers and I started one about it here.

As to sport package, I drove one with and own one without. I wouldn't classify it as a must have, but it's nice. I still think that the non handles like it's on rails, especially considering how high it is from the ground.

As for options, I have most. I love my HUD and active ventilated seats, but those are rare to find used. Comfort access rocks, but not a must have for me. Cold weather I wouldn't live without. Third row seats are nice, but cramped. Premium audio is awesome, but I could live without it. NAV is nice, but so are garmin systems. Integration of nav with HUD is pretty awesome though

For me, the options would list from must to least have would be:
Cold weather package
Active vent seats
Tech package with HUD
Comfort access
Third row
Premium audio
NAV
Rear seat entertainment (decent option for kids on long rides, but I hate the screen on the armrest)