It cost a lot of Starpoints (10,000 or more) to redeem a night at SPG Category 4 or higher Hotel which it almost don't make sense unless you need to top up a small amount.
This is, however, a good way to purchase partner airline miles at reasonable price. Every year, I buy the maximum amount of Starpoints which is 30,000 and convert it to frequent flyer miles. SPG have a large variety of airline partner and allow you to convert on a 1 Starpoint to 1 mile basis on most airlines.
When converting Starpoints into airline miles, there is a throw in sweetener; when you transfer 20,000 starpoints, SPG will add 5,000 extra starpoints so in total you receive 25,000 airline miles of your choice.
It cost $0.021 per mile if you factor in the 5,000 bonus when purchase 20,000 starpoints. The flexible ability of transferring Starpoints to many airlines frequent flyer account is a great feature of SPG. Some airline may not sell miles directly but you can purchase Starpoints then transfer them to top up your account.
The current sales is open to all, you do not need any SPG status to buy. You can purchase a maximum of 30,000 Starpoints per calendar year for your account or receive points as a gift. The account that receives Starpoints must have been open for a minimum of 14 days.