My advice is to go for the platinum warranty if you decide to buy. And make sure you buy longer term if you don't plan to hit 100k miles within a shorter warranty period as most parts wear out based upon mileage, not time.
Since our OEM warranty expired, we've had 2 major repairs on our 330i. The first cost $400 at our local indy shop, the second was $700 - if you go to the dealer you can add +$200 each. Neither would have been covered by the powertrain warranty.
So we are still ahead of the game at the 74k/5-year mark and counting.
1993 325i - gone!
1997 328i - gone!