I'm in same boat with my 09 e92. Great car and very reliable but close to 50k mark. On these forums you read more about the bad than the good but you also can educate yourself on the items most likely to fail.
Not all extended warranties are the same, the BMW ones offer zero pro-rated refund if claims have been paid. Pay 3k for 3 years of coverage and car gets totalled out after small claim and you are out of luck. Most 3rd parties reduce by claims then pro-rate on time/miles.
Take the time and read the sample contract before you buy anything. Most will frown on ANY mods and can (will) use wording in contract to deny claims. One I saw required oil changes every 5k miles or 6mo. Not a huge deal but again if not followed you will be SOL.
I plan on keeping mine another year and believe will be easier to sell as all warranties can be transferred for small fee. If not private party sale and I trade in I can cancel and get some refund.