I don't think you spend money to up vote peoples posts. It's possible but that requires more reading on my end as well.

I'm not too sure if STEEM POWER comes out of your account

STEEM POWER is more like "account power" that can be converted into STEEM to cash out, or you can buy STEEM and convert it into STEEM POWER to give your account more control over curation rewards causing up-votes to give more curation to the author, or down-votes to take more rewards from anothers post.
I think the longer you hold onto STEEM POWER it gives your account more power.

And STEEM DOLLARS I think can appreciate in value and might also be affected in some way by STEEM POWER but I don't know exactly how it works.

I also think that up-voting other peoples content can lead to giving you some rewards as well.