Cash & Points rates, especially outside the US, often make a Starpoint purchase worthwhile.

Consider a room available prepaid for €200 or 4000 points + $60. (I just found that rate in Germany.) You could pay €200 = $285 and earn 1925 Starpoints (by paying with an SPG AmEx, and choosing the platinum 500-point amenity). Or you could buy 4,000 Starpoints and pay $60 (and choose a different amenity).

So for the 6,045 Starpoints you buy or forgo, you save $225, making each Starpoint worth 3.8¢, which is more than the 3.5¢ you can buy them for.

Or, if this is your only Starpoint transaction and you aren't concerned about forgoing earned Starpoints, you can get a $285 room for $200: $140 for 4,000 Starpoints and $60 for the cash part of the Cash & Points rate.