First of all: Steem is currently worth under a dollar.
So you have a cheap buy in. Just weeks ago you had to pay 1.5 times as much for the same amount of steem!
The second reason is, that you can earn kind of an interest. Yeah I know, steemit doesn't pay interest at the moment.
But with higher steempower comes higher value of your vote. Some will say now: I won't upvote my own blog!
No problem, delegating your steempower can bring you an similar income. So you don't need to upvote yourself!
Here one example:
If you buy steem power for 100$, your vote will have 0.01$ more value. You can vote 10 times a day with 100% without losing votingpower. So you can upvote yourself with 0.10$ a day.
If you leave out the 0.70$ you earn in the first week and think of a stable exchange rate, you come to this calculation:
100$*1.001^358=143.02$
100$ investment and 43.02$ earnings in one year.
This would equal an interest of 43.02% per year!
Every fluctuation has an impact on this number! If steem gains value, you will have additional earnings, if it loses value the earnings will shrink.
If you delegate your steempower it will be different. But for example minnowbooster offers roughly the income of upvoting yourself.
The third reason is, that you will get more attention due to your steempower.
They will hope for refollows, upvotes on their comments and blogs and high curation rewards.
So independent from your own votes, you will earn more with your posts without doing something else different.
But remember: Never invest money you can't afford to lose!
Happy steeming!