Just looking at the numbers, I pretty much purchased most of my Steem and Powered Up - 800 SP on day 28 here. I earned a few, but not much compared to what I purchased.
However, we must keep in mind the power of compounding - my 800 SP gives me $0.13 per upvote and my votes are replenished at 20% each day - depleted at 2% per upvote (at 100% for 500 SP and higher).
That is $1.3 per day * 365 = $474.5 per year. This is at a time that Steem is depressed in price and my account is less than $2,000 in value.
Without compounding, the return, if I can give $1 worth of upvote and get $1 worth of reward in return, my rate of return is 2.37% per year.
If and when Steem goes up in value, my rate of return will increase geometrically / increasingly.
That is just simple math - not counting the growth in followers and people who will collaborate or reciprocate.
All the best!