Better steem power (SP) help the account to get more populated account as there are lots of account who has more than 1 lac SP which are earning more than 1000$ per post so yes this could be the point that better SP helps our account to get populated and help us to get more upvotes.
With better SP you can have many option to do like you can donate your SP on delegation to any whales and it can return you with higher upvotes value as well as if whales enter into your account yu can get a better reputation .
As reputation doesnot matter in steemit but the audience are attracted more if user has a better reputation and this cone with the proper usage of voting power they have.
Steemit power you can buy from delegation from block trade and also can take sp with your cryptocurrency coins.
Better sp can make your account grow faster as you can take example of musing as it has better SP then the voting value of steemit if it upvoted with 100% will be more than 8$ per post than you can inagine better SP will get your account more populated and more rich in plenty of time.