Good question, and IMHO a relatively simple answer. If you plan on keeping the car (especially beyond 2 more years) and you cannot afford a major repair then get an extended warranty. Just think how much a tech chasing an electrical problem will cost you!

There is no reason why your car might be more or less reliable than another X5. There are plenty of posts on the forum listing X5's with 100,000+++ miles in addition to the complaints here and there of problems (which quite honestly are still pretty rare I would think...keep in mind BMW has sold hundreds of thousands of X5's worldwide (http://www.worldcarfans.com/9090115.017/bmw-x5-celebrates-10-years-of-success). There are only a small number represented here on the board).

Most of the problems you've had a typical of many cars. A few might be more common with the X5 or BMW's in general, but honestly so far they are not too bad.