I can't say much for minnowbooster and smartsteem. But the bidding bots depends on how many and how much they are betting. At one time, I got almost 1-1.5SBD in return for using the bot. The only problem are people who are betting at the last minute with a very high bid, say 50SBD with no regards to the max profitable bid making the ROI negative. Still I do think it is good for minnows to increase what little visibility they have. Also half of the vote goes to SP so you're voting power increases slightly.