According to my calc, buying the upvotes is more profitable.
I did spend 750 DEC today for an upvote. The upvote was worth $1.285. So after curation this would be $0.96375. Converting this to Steem with a value of $0.25, this would give me 3.855 steem.
When selling the 750 DEC at the median between highest buy and lowest sell offer (0.0045), I would get 3.375 steem. But when withdrawing it I will have to pay 5%, so 3.206 will be added to my steem account.
Maybe I am doing someting wrong with my calculations, which is always possible.
What level of summoners do you think is necesarry for reaching Diamond III?
I haven't done the maths in a while but when I did it was showing selling DEC to come in ahead of buying votes. I might try it again when i've time as prices change over time.