Buying Steem is theoretically a bad idea as inflation would normally drive the value down by 10% annually. Converting to Steem Power is good. Steem Power gets interest to combat inflation (like buying a US savings bond).

Two benefits of converting to Steem Power:

1. it gives access to voting pool which helps you earn money blogging and obtaining followers, or you can rent out the voting power and gain additional interest.
2. Steemit is expected to explode in popularity like other social media platforms before it. This explosion in popularity will create a demand for Steem that will seriously outpace supply of Steem.