If I understand your question, you need to exchange the SBD to Steem before you can power up. You can directly power up from SBD with a service like Blocktrades. SBD has a little utility because you can use them to pay for certain services/give as gifts here on the platform, so it's probably useful to keep some "change" around. As for the price, it appears to be dropping ATM. Powerful forces are moving the value down, so we'll have to see what happens.