I think the vote bots/buyers (for the most part) are not adding any REAL value to the steem ecosystem. In fact, I think it's actually harming the system, to what degree, I know not. High SP holders are just leasing their VP for a nice profit at the expense of no longer manually curating for quality, as well as no longer being the (proof of brain/human) deterrent to the ever growing list of spam/scam-mers who seek to profit/siphon off the system with as little work/input as possible.
The promoted tab should be fixed/incentivized for those want to promote themselves or others INSTEAD of using bots. The SBD used to promote a post is burned (sent to @null) and overall helps increase the value for everyone.
IMO, it's very similar to an aspiring "Youtuber" that WANTS to get organic views/subs./likes etc. but instead of just creating valuable content and interacting with the community, they decide instead, to pay money to an army of "bot accounts" for artificial views, likes/upvotes or comments on their videos for promotion just to have the "appearance" of a legitimate/popular channel/figure, in hopes of getting noticed by the community at large. This is probably already happening on Youtube. The difference here on Steem is that everyone here is affected by everyone else's actions due to a shared rewards pool.
In short, using bots for upvotes or (ROI ESPECIALLY) sounds like the worst idea forward if quality, originality and genuineness are our main concerns.