I will say that @bumper has been the most consistently effective bot I've used. It's a 3x return (minus curation pay-out). That being said, you can't send more than .5 SBD, so it's not a bot that anyone can use to really rig the system. At least in my view.
I've found that most of the bid bots on steembottracker are usually a losing game. Unless you get very lucky, by the time the bidding is over, you're likely to have lost some steem.
The main thing for me is whether or not bots help elevate my post to a point where readers can find it. You make an interesting point on how that's a double-edged sword.
Thanks for the post!